approach for and good tips for mentioned scenario

Please give the steps for above.Can you all please share views for below scenario and share you approach.

1.Let say unix team compalined at OS level oracle is using more cpu.

In server 9 databases are running.

How I need to approach on this scenario.

-->how should I catch that particular pid and from there spid,sid and sql etc..

-->should I focus only on foreground session eliminating background level.

Please give the steps for above.

2.Let say unix team ompalined at OS level oracle is using more memory.

-->how should I catch that particular pid and from there spid,sid and sql etc..