When i did y= and put in -x+3 for Y1 and (x-1) divided by -3 and hit graph, it says ERR:SYNTAX please help. im trying to solve linear systems by graphing.

Try rewriting your equations in the equivalent forms that follow.
Y1=3-X
Y2=(1-X)/3

If you do not get a syntax error it means that you were not using the correct minus sign.
If the - is the first symbol after the equal sign you must use negation (-) or change sign key.
Similarly, after the division / key you must use the negation or change sign (-)