How to do you create subjunctive in the present tense?

First of all take the word in the infinitive (e.g. comer/ hablar/ vivir) Then put conjugate it into the first person singular (e.g. como, hablo, vivo). Then take off the "o" ending. If it is an er/ir verb change the ending to and ar verb ending (e.g. coma/ viva) whilst if it is an ar verb change the ending to er (hable).