If you’re talking about the -1.72 or +2.31 that show up within the bar to the left during analysis, it refers to the sort of lead one has valued in “centipawns.” So, +1.00 essentially means white is winning by a pawn and a score of -2.11 means black is winning by little more than two pawns. The fractions come from piece activity (field position of the pieces, if you will). Restated, black and white may have equal material, but if the black queen and king can be forked by a knight and the white pieces are safe, that number will be favorable to white.
That number is also how the computer assesses inaccuracies, mistakes, and blunders. So, you’ll see a lot of fluctuation in that number between moves at lower levels (with more blunders) and fewer at the GM level.
Ive been playing a couple of games with my friend and we cannot figure out what the numbers on the side of the screen mean. Are they a score? If so, what's good and what's bad?