how can I fix my chainsaw?

Could be a number of issues. Check air cleaner, change spark plug. Check fuel filter, if in doubt change or blow it out with compressed air (inside to outside).
High speed mixture screw may need adjusting to richen up fuel mixture. If saw is old or sitting around for many years crankshaft seal may be worn and leaking. There maybe an air leak around the carby check that mounts are secure.
Always remember: two strokes need fuel and spark to operate check these first.
Good luck

onyamichael
February 2013