How to shorten trouser

Can anyone explain to me or point to a website which shows how to
shorten trousers.  I can give $16 to the local rip-off korean
laundry/altering shop who use a machine and do a butchering job... but
I would like to know how I can do it myself or buy some machine (maybe
a hand held sewing gizmos) that might help me do that?

thank you!