so a common denominator of 1/2 and 2/3 is 6 (sometimes the best thing to do is multiply the two denominators that are liitle numbers lol and bam that's a common denominator)
this means that (1*3) / (2*3) and (2*2) / (3*2) to get to the common denominator
the fractions become 3/6 and 4/6
Hope this helps ;)