Thanks for trying. I also have no idea, it's been a while and I didn't need either of those words once, just used it to illustrate a rather annoying position ESLs can be put in.
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.