The concept of time (tense) can be differentiated into three categories.
The present / simple present tense. (what are you presently doing )
The past.(What you did some time back).
The future. (What you will do some time later).
And all of these tense are differentiated into the following four categories.
1.Indefinite Tense
2.Continuous Tense
3.Perfect Tense
4.Perfect Continuous Tense