To answer your question specifically, if it has a bam, bas, bat, bamus, bastis, bant at the end it means it is imperfect. The BA shows that it is an imperfect verb and the personal endings are just added on. It will be translated with a _____ing. Most verb tenses have slight variations of the endings. The endings you listed O,M,S,T,NT are those for the present tense. When you learn mood there is a different set of endings to learn too. If you are taking or learning Latin the Wheelock Books are great textbooks.