Legal Question in Civil Litigation in California

If you don't know what you're doing, you have no business filing anything with a federal court. Contact a lawyer. Normally a declaration under penalty of perjury will suffice.

Mr. Stone is right. Just by asking the question you asked, you show your lack of understanding of what you are doing is so great that you are likely to totally screw up if you don't get a lawyer's help. Affidavits are not filed "under oath." In fact we pretty much don't ever use affidavits at all in California. We use declarations under penalty of perjury as Mr. Stone said.