how do you know how many times to strum the uke in each chord?
To answer your question directly, you know how many beats (strums) to use by listening to someone else play the song, and then duplicating the number of beats they use.
In your Hey Jude example, I recall four beats with the word
Hey on the third beat of those four,
then four more beats with the name
Jude on the first beat of those four,
and four more beats with the syllable
'fraid on the first beat of those four.
I know that because I've heard the song and heard the beats. If you can find/read sheet music you can see where the beats are supposed to fall.
Other songs have different rhythms. A waltz has three beats per measure.
Chord sheets are useful to show how to shape and position your left hand.
Tabs are useful to show which strings to fret with your left hand and to pick with your right hand.
Sheet music (notation) shows both pitch and rhythm. All of these are useful.
Too many Web pages claim to provide a tab when they are actually providing only chords and lyrics. Once you learn the difference you won't be fooled when someone mislabels a page.
Google Guido Heistek.......hear the strum. He has a great DVD on strumming. On his youtube channel you will gleen enough to have a good concept. His "learning to strum" on a piece of cardboard is brilliant. Teaches you how to become instinctive with strumming
Thanks for the reminder. I had bookmarked Heistek's site a few months back, then got distracted by fingerpicking techniques. You are absolutely right, this is an excellent resource, and I need to spend some more time here.
http://ukuleleinthedark.com/ud-28-strum-like-a-drummer-backbeat/
http://ukuleleinthedark.com/paper-strum-strum-without-a-uke/