How do I form the conditional?

It's easier than you think! The basic rule for forming the conditional is 'future stem + imperfect tense ending'.

So to form the conditional you need to take the future stem (which is usually the infinitve) - we're going to use manger, but it's the same technique for all regular verbs. Then you choose the imperfect ending which matches the person doing the verb in your sentence. So:

je mangerais               nous mangerions

tu mangerais               vous mangeriez

il/elle mangerait           ils/elles mangeraient

There are some verbs where the future stem is not the infinitive. To form the conditional with these, you follow exactly the same rule, except that it's important to remember that the future stem is not the infinitive. A few key ones to note are:

être = ser

avoir = aur

aller = ir

faire = fer

Then you just add the same endings as above!