The numbers are an attempt to sum up the relative positional imbalances in terms of "pawns."  So you could say, if you were White, I were Black and the score was +0.06, that you were up 6% of a pawn.  Of course, computer analysis is extremely finicky, so such tiny numbers probably shouldn't carry much weight.  But if the computer says you're up (or down) by at least 0.50, I'd say that's significant.

The sign on the number just indicates who is theoretically up; positive numbers favor White, negative Black.  At least, that's the convention adopted by this site (and thus by my converted analyis); my chess engine scores each move relative to that player.

How do you interpret the negative numbers.  Is that on a scale of -10 to +10?  I guess I'm just wondering how this works...