How to transfer my itunes to a new computer?

I have an Iphone, an Ipad and an Ipod, but most importantly, I have a large collection of songs on itunes that I started many years ago when I got my first ipod. In the past when I had bought a new laptop, It has not been easy to transfer my music, as a matter of fact, a couple computers ago I lost the many hours I had spent to rate my music, cuurently my itunes library does not even has the all playlist that I ones dedicated so much time to integrate. Whatever.

I say ther must be a right way to transfer my library to a new computer, and I want to learn.

Can anybody help me?