Simple tenses consist of 4 types. First, the popular tense is

Simple Present Tense.

This tense explain about general fact and habitual.

Ex           : I go to school every day (habitual)

The sun shines in the day sky (general fact)

Simple past tense

This tense is same with SPT, just the different is explaining the past time.

Ex           : I went to school yesterday

Simple Future Tense

It explains about future.

Ex           : I will read it soon.

Simple Past Future Tense

It has similar form with SFT, but the modals are changed by V3. Like as, will=would, shall=should, may=might etc.

Ex           : I could get freak