Past, present and future are the three main verb tenses in the English language. The future tense indicates what is going to happen. Keywords such as tomorrow, next year and later are signposts that future tense is being used. The past tense describes events that have already occurred.
Words such as yesterday, last week and earlier are indicators that the sentence is in past tense. Present tense is used to talk about events that are happening in the moment, or that are continuous.
Each verb tense has a subset of tenses: simple, perfect, continuous and perfect continuous. Simple present talks about what's happening right now, simple past discusses what has occurred and simple future discusses what is to come. Each subtense has a set of rules that determine when it needs to be used.