my best shot before looking it up: a deposition is a collection of your sworn testimony in like a pre trial context and an affidavit is a declaration of .. something that you confirm? after i looked it up i see no reason why we have two words for this
Fundamentally? Depositions are created through an adversarial process while affidavits are created through cooperation. If you get robbed, you go to the police station and swear out an affidavit as to what happened. If you are accused of robbing an insurance fund, the lawyers gather around and record your responses to hostile questioning. Both create legally-significant records of an event. You want to swear out an affidavit, you do not want to be deposed. If you are contemplating this question without a lawyer to explain it to you, your problems are direr than your English proficiency.