How does the WEP protocol work?

Question

Computer networks

Hey!
Recently I flashed the asus on TomatoUSB, I decided to dig deeper with security. I started from scratch, so I decided to use 40 bit WEP.
Questions immediately arose: why can't I connect via passphrase and why only the first of the 4 keys below works?
2) What do these 4 lower keys mean, why are there 4 of them, are they "guest" and what formula are they used to calculate?
3) Does WEP break so easily without active clients?

Answer 1

https://en.wikipedia.org/wiki/WEP

Answer 2

3) Yes, you can't use it.
for example here