Tables-Primary Key-Sequential read

Hi Folks,

Out of the following which imporves performace?

1.Using all the primary keys of a table in the where clause of a select statement?

2.Using any one or two (not all) primary keys of a table in the where clause of a select statement?

Let me the know the same in the case of using an Secondary index.

3.If we follow the second one,then it will go for a sequential read,how this sequential read mars the performance?

4.How creating an index will affect the database as BASIS guys are not in favour to creating an index.

Thanks,

K.Kiran.