#1
How do you Push in the frets? Do I need a tool or can I do it by hand?

EDIT: I'm talking about the act of placing them in the fret slots.
#2
By hand if your a body builder maybe. They are usually hammered in, no not a regular drive nails hammer. Or pressed in. If your asking this question you may be way over your head trying to put frets in a guitar. Theres alot of tools involved in doing this job. And a pretty steep learning curve do a remotely decent job.