client is created (questions )

hi friends

i have few questions.i am new to basis can any one help me?

1 what is client ?

2 how many clients are created in landscape ?

3 where the we have to create users and clients ?

4 how to copy local client and remote client ? (in detail step bye step)

5 what is client export and import ?(in detail step by step )

6 what are the t-codes used for above questions?

plz help me friend

thanks in advance

by nani