Compared to other languages like English, Portuguese has a high number of verb conjugation forms. If you don't know the subject pronouns yet, it is best to learn those first to understand what is meant by first-, second- and third-person.
Portuguese is classified as a pro-drop language. This means that the subject of a phrase can often be omitted and implied by context and the verb conjugation form.
Moods and Tenses
Mood refers to whether the expression of the action is intended to be factual (indicative), desired or conceptual (subjunctive), mandated (imperative) or used as another sort of modifier.
Tense describes when the temporal aspects of the action such occurs whether it takes place in the past, present or future. It can also refer to whether the action is habitual or lacks a definite completion such as with the imperfect tense.