Hi, new here i hope you can help

My teacher just explained viewing rectangles today and I still don't get it. I know the TI can do it for me but I need to learn how to do it by hand. I thought if somebody different explained it it might make help.

Ex: f(x)= Square root 0.1x+20

f(x)= cos(0.001x)

Thoes two are just a few of the problems i'm stuck on.