Can somebody tell me something about renting servers, buying them and leasing them out. Thx.

Anybody?

Renting servers you probably mean Dedicated Servers
Buying them you probably mean Co-Located Servers
Leasing them out you probably mean reselling dedicated server
or if you have your own NOC renting them out.

I could've just totally twisted what you ment out of proportion
but if I'm wrong please do correct me. Then we can go into
these topics futher ;)