The hard part is knowing which tense to use, or which form of
the verb. But it doesn't do you much good to know that, if you
don't know what the forms of the verb are, or how to spell them!
That's the easy part, but you do have to take a little time to
learn the rules. Most grammar books have a summary. Study one, (or
study these spelling rules and these irregular verb forms), and then take the "mini-quiz" below: