(Skip to the bottom for the short answer.)
The F refers to the root of the chord. If you were playing Cmaj, C would be the root. Then you add the 3rd and the 5th. For Cmaj, count up from C: C, D E is the third. The 5th, also count up from C. C, D, E, F, G is the 5th. Thus, the triad looks like this: CEG. You can add an extra C on top too, for CEGC. Or, the lowest note can be E, which would look like EGCE.
You can spread them out like this:
E G C E if you like. It is all the same thing.
If you had Cmaj7, you would add the 7th on top. C, D, E, F, G, A, B. So the chord is CEGB. You could do the 9th too. CEGBD. 11th, CEGBDF, 13th CEGBDFA, 15th, CEGBDFAC.. Ok, too far.
So! Fdim7. You need to know what a dim7 is. That's harder.
But the short version is F, Ab, Cb, Ebb. This is probably the reason you're having trouble. A lot of people will tell you that Cb and B are the same thing, but assuredly, they're not! Same for D and Ebb.
Fdim7 comes from the Gb minor scale, Gb Ab Bbb Cb Db Ebb Fb Gb. You can raise the 6th and 7th degrees in in a minor scale for melodic and harmonic purposes. So you can get an F from the Fb and a Eb from the Ebb. So, raise the Fb to F and get F Ab Cb Ebb! Ta da!
Ok. buuuut, the exciting thing about Diminished chords is that you can switch them around in a way that I don't think I can explain. But ...
D F Ab Cb
B D F Ab
G# B D F
are all the same chord.
You can use a Bdim7 instead of a Fdim7. It will sound exactly the same.
How on earth does one play a Fdim7 chord? I don't have enough solid knowledge of music theory to put it together for myself (slept through that class in high school I guess)
Also, can someone explain to me what the 7 means? (oy, yeah if someone could explain the theory behind it I'd be indefinitely grateful!)
--Cashew
PS== After some playing around, I'm playing it as 5454, is that near correct? (sounds ok to me, but i could be off)