The numbers in a table file tell you what numbers represent the letters of the alphabet when you open a particular ROM up in a hex editor. Every bit of information in the game is stored as stuff like "DF 00 49 31 0A" regardless of what it pertains to. But in the right context some of that nonsense will represent the letters of the alphabet and since the alphabet is in a specific order it should be a set pattern. Once you figure out part of the pattern the rest should come easily.
The patterns represented in a table file are game specific. For example: some games may have 00 represent A (in the right context because remember, everywhere else in the ROM 00 would mean something completely different). If that IS the case you can pretty much bet that B will be 01, C will be 02, etc. In another ROM the alphabet may start at 3F = A and then continue on to 40 = B, 41 = C, etc. These are just random examples off the top of my head.
EDIT: I'm not an expert but I think this is right for Mike Tyson's Punch-Out.
Inside the ROM, 64 looks like a square and 65 looks like a circle. Wasn't sure what to put in those spots. Also, I don't know what they're called specifically but 5F is the mark that goes at the beginning of a quote and 60 is the type that goes at the end. I only had the second type on my keyboard so I didn't know how else to represent that.