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At the very top of the chart is the title of the song, followed by the suggested key, though the very point of numbered charts is to make it each to change keys... in all likeliness, this will be called just before the count... be prepared to switch on a dime!
Below the key is a hint, usually including the time signature -- how many beats each number represents. In this case, "Ray Price 4/4 shuffle, walk bass." Now hopefully this means something similar to everyone -- in this case, play a walking bass, drummer plays a 4/4 shuffle, and everyone counts the chart in 4 beat measure; i.e., each number stands for 4 beats. Other possibilities might be "2/4 country shuffle" (eg. Buck Owens "Kansas City Song"), "Johnny Cash 2 beat" (eg., "Folsom Prison Blues"), "4/4 Straight 8's" (eg. a rockin' version of "The Race is On"), "2/4 Waylon" (eg., "Good Hearted Woman"), etc.
I write charts without repeats. As I've played many gigs from charts, I found the hardest part is searching through the chart for repeat points, codas, etc. It's much easier just to write the whole thing out -- that way your eye doesn't have to move away from where you're reading. Occasionally on songs with very easy changes such as a blues, I'll omit the numbers and just put [Verse], [Chorus], etc. However, generally, I like to write down all the numbers. Sometimes, any little bit helps and you'd be surprised how a little pressure -- like 12,000 people watching -- can make the easiest changes suddenly disappear into nowhere.
The numbers are based on the scale tones. For example, the scale tones in C major are C(1), D(2), E(3), F(4), G(5), A(6), B(7). So a "1 4 5 1" intro in C translates to C-F-G-C. Transposed to, say, F, this is F-Bb-C-F. I mark minor chords with a lower case 'm', for example '2m' in the key of C is a D-minor. Other flavors include 'dim' (diminished), '7' (7th chord... this is a superscript in case it's hard to tell in this text), '+' (augmented). I seldom include advanced chord mods on my number charts, preferring to leave these to player's experience.
I often write out rhythmic or phrasing notes. For example, on a legato section, I might write "follow vocalist". Common shorthand marks include: 'X' (stop short... no ring), '<>' (break, but hold), '^' (hold till cue... fermata).
I have a personal shorthand to remind me of endings. Because I used the computer to pound out quick charts, I don't have standard music notation available, so I abbreviate using letters. O=1, T=2, R=3, F=4, followed by a lower case 'a' for the "and-of-whatever". For example, a 'cha-cha-cha-cha' ending would be (OaTa). Or a more standard 'cha-cha-cha' would be (-TaR).