i have a macbook - 2012 and the ssd is full - only 32mb free - i cannot boot up . need to delete files but how?
yes, space is certainly an issue.

can you put this into target disk mode with a fireire or thunderbolt connection to another mac?  this is relatively user friendly if you have another mac around and a connection between them.  

do you have a recovery partition on this machine?  is that how you got to disk utility without being able to boot?  

you could boot into this and use terminal to remove some unneeded files to make it bootable/repairable.