The 'Mandatos Formales' (A.K.A. Formal commands) are commands for the 'tu' and 'ellos/ellas/ustedes' verbs.
To form the verb into the formal command do as follows:
1. put the verb in the 'yo' form. ex: bailo (bailar->bailo)
2. drop the 'o' at the end of the 'yo' verb. ex: bail (bailo->bail)
3. switcheroo
There are 2 types of switcherooes for the commands and that depends on the verb's original ending so...
a. for verbs that originally end with 'er'/'ir' (ex: hervir), replace the ending with the letter 'a'. ex: hiervo (for this example since its stem changing you have to replace the 'e' with an 'ie' [its just a rule] )
b. for verbs that originally end with 'ar' (ex: bailar), replace the ending with the letter 'e'. ex: baile (and there is no stem change here)
Now finally, if you are talking to one person (usted), leave the verb as is, but if you are talking to two or more people (ustedes), add an 'n' to the end of the verb (ex: baile->bailen) and that's it!
For (more/a refresher) about stem changing verbs, look at the attachment for a link to brief video explaining that (sorry couldn't directly put it here since it doesn't work)
And as always, have a good day!