If you have just bought a ukulele and want to get started, and this seems like garble, start with the physical training, use the exercises and simple tunes to train your fretting and strumming fingers to accurately and smoothly find the right fret and pitch. Just leave this post until you have developed your physical fretting and strumming. Then apply some intellectual effort to learn the 48 notes and pitches on your fretboard. Learn them well enough to be able to identify the Blues boxes on your ukulele fretboard. When you get to this stage, you have all you need to get started on learning to play the Blues. Find the information about the tunes, scales and chords and stuff and apply it to make your own Blues repertoire. There is no need to read on if you are not ready yet.
Why do people take time to learn scales and keys?
Many famous blues players claim they have no knowledge of music theory. This usually means they can't read standard notation. But, they will know where all the G notes and Bb notes etc are on their guitars, and they will know the boxes or scales used to play the blue genre music. So in actual fact, they know a lot about the practical application of music theory, but just never learned to read Standard Notation. Also it is not cool for Blues musicians to be publicly knowledgeable about music theory, there are so many critics waiting to pull them apart that they avoid the stuff about the theory and just play the music in public. Maybe in rehearsal and band meetings they operate differently and will use the labelling and theory stuff?
If you do not understand the following, there is nothing to stop you surfing around and finding explanations and stuff so you can understand it. None of it is rocket science, you are allowed to get a notebook and actually write stuff down so you remember it and can keep looking at it to work it out. You do not really need to buy a "Blues Ukulele" or "Blue Ukulele music" if you can learn the 48 notes and pitches that exist on the 12 frets of your ukulele. You can work out a lot of stuff for yourself and then work on it and make your own Blues sound.
As a ukulele player, you may never bother to learn how to read Standard Notation, but that is not an excuse for never learning the notes and pitches on your fretboard and how to put them together for your favourite genre of music. The blues genre has specific scales and "boxes" on your ukulele fretboard. If you are serious about the blues you need to learn them.
The next step is to look at Blues Players. One of the most contemporary Blues/Rock players is Keith Richards. When you study his music and playing, he only have 5 strings on his guitar. He and many others use a scale called the Major Pentatonic or Southern Blues Scale, which is based on an altered G major scale. You can look it up and then find the boxes where it is on your ukulele fretboard, in any tuning you choose to use. However, Keith has made it easier for himself, and has copied his predecessors and Blues heroes, to tune his guitar in X G D G B D . If you have a baritone ukulele, you only need to drop the E string down to D and you have almost the same set-up as is used by Keith Richards. So you should be able to access a lot of Kieth's material and the material of his Blues heroes with a Baritone ukulele, with the E string dropped to D. You can check all the other Blues players and do what Kieth and Mick did, study their guitar heroes and work out the music, without lessons or learning how to sight read. When they were doing this, there was no internet to surf around, now everyone reading this can check out a famous blues player every day just by surfing around.
Another thing you can do is look at another very popular Blues instrument, the Diatonic Harmonica. Look up "Second Position" harp or harmonica to study the notes and chord constructions often used for Blues genre music and apply it back to your ukulele fretboard. You could discover that the best key Harmonica to play the most common Southern Blues scale is tuned to C and played in the Second position? So look at the notes on a Marine Band Harmonica in the key of C, the low C is C4(SPN), exactly the same low note as you have on your re-entrant tuned ukulele. And you can map the notes on the Marine Band along your ukulele fretboard. So you should be able to get some harmonica music in a format you can read in the key of C and translate it to your ukulele fretboard.
Other Blues instruments also exist for you to study.
Tuning like Keith or translating from the harmonica or using a Guitar TAB is just the first step. If you can't get the low notes like you have on a guitar, or get the wailing sound of a harmonica, your ukulele blues may sound thin and squeaky and not very credible. So you need to learn the next piece of knowledge, how to make it sound like the blues on your ukulele. This is where you need to learn about chord inversions and voices. You will be using the same Blues scales, but you need to re-arrange the notes in the chords to get a credible Blues sound. There are only 3 inversions to learn for chords, its not rocket science to write out the notes in the chords you want to use and and the 9(?) possible combinations to work through the sounds of the chords and find one which has the right sound on your ukulele. You can also look at the open tunings, which make the chord playing much easier on the fretting fingers, but you have to re-learn the fretboard.
As discussed in posts above, a lot of "Blues" you hear played on ukulele is thin and squeaky and maybe lacks credibility. You can adapt stuff from other instruments, but you need to work on it to get it to sound like credible blues on your ukulele. If you are really keen on playing the Blues, maybe that is an opportunity to follow in the footsteps of the great players, you do not ever need to learn how to sight read Standard Notation and you can say that you therefore do not know any music theory. But, you do what they did and learn your fretboard and learn how to construct chords on your fretboard and learn how a Blues tune is assembled. You do not need a special ukulele or specially arranged music to achieve this, you can just surf around and find the information and apply it to your fretboard, and then work out an arrangement and play it 100(?) times to perfect it for an audience.
If you have just bought a ukulele and want to get started, and this seems like garble, start with the physical training, use the exercises and simple tunes to train your fretting and strumming fingers to accurately and smoothly find the right fret and pitch. Just leave this post until you have developed your physical fretting and strumming. Then apply some intellectual effort to learn the 48 notes and pitches on your fretboard. Learn them well enough to be able to identify the Blues boxes on your ukulele fretboard. When you get to this stage, you have all you need to get started on learning to play the Blues. Find the information about the tunes, scales and chords and stuff and apply it to make your own Blues repertoire.