Could / Can

[jack]

Are these correct? What do they mean?

1. I could take a shower right now.
2. I can take a shower right now.
3. I could have taken a shower right now.

[jack]

What do these mean?

1. How could I help you out? (If this is wrong, why? 'Could I help you out? ' is correct?)
2. How can I help you out?

Thanks.