Sugar canes need to be near water, just plonk down some dirt underground and plant those sugar canes near some water ;p

so do i just cut some down, then plant them back in some dirt?

Yup, they can grow to a max of 3 block height, then you can just cut everything but the last block down and replant the 2 that you cut down.

Make a nice room and then Put dirt on the side and then water then dirt , water , dirt and so one then you just plant your sugar canes on the dirt

You can also do this with everything else

ok next question is can some one tell me how to make a underground tree farm? with pictures this time would be good

Same as but you need alot of space (4 blocks in each direction) and light sources....either torches or lightstone.