Most of the time "affect" is used as a verb and "effect" is used as a noun. This is not always true, but the times where they can be the other way are rare and you should not worry about them - native English speakers do not.
Usually, "affect" means "change" or "impact" and "effect" means "result." There are exceptions to this rule, however.
The weather will affect our plans.
The effect of the storm was that we had to cancel the game.
The tragedy affected everyone.
As an effect of the tragedy, three people are dead.