Affirmative commands, go!, do it! etc. in the second person singular are formed, if it is a regular verb, by taking away the final s of the infinitive or with the 3rd person singular, but in both ways we get to the same result. As always, this is a very stable rule in all languages, the most frequent and most used verbs are irregular.
All other affirmative commands and all the negative commands, don't go, don't do it, are formed with the conjunctive. Since the second persons singular is inexistent in Brasilian Portuguese things are simple in Brasilian Portuguese. The imperative is identical to the conjunctive, see 12.1.1.
In the following sentences most of the commands are irregular. Choose the right option. The person to use is indicated. In the sentences we assume the European Portuguese. In case that it is second person singular choose therefore second person singular and not, what would be correct in brasilian Portuguese, the third person singular.