Someone explain open source to me please.?

What is the motivation for people to write open source software? Who pays the developers that wrote linux? I understand why people write small open source programs, but who would spend all that time to get nothing in return???
I know what open source is, I’m in college to be a programmer……I guess what I wanna know is, do the developers of linux get paid??? If so who pays them???? How was Linux financed???

what is the number of developers for Linux?

hi, how many people is involved in developing linux, ubuntu, open source software?, been looking but i want to know how many developers are doing this great things


What im asking is:

Is it as easy to use as microsoft XP?
Is it an easy transittion if ive previously only used XP?
Is it only for developers?
Any good? Worth downloading/using?