It describes an action in the past.
(+)REGULAR -ED ENDINGS OR IRREGULAR VERB LIST
(-) DIDN'T + INFINITIVE
(?) (wh-)+ DID + SUBJECT + INFININIVE?
When Homer got up, he felt thirsty again.
Used for predictions and decisions taken at the moment of speaking.
(+) WILL + INFINITIVE
(-) WON'T + INFINITIVE
(?) (WH-) + WILL + SUBJECT + INFINITIVE?
If Homer goes on like this, he will have a heart attack.
It describes a routine or habit.
(+)INFINITIVE (+S FOR 3rd ps)
(-) DON'T or DOESN'T + INFINITIVE
(?) (WH-) + DO/DOES + SUBJECT + INFINITIVE?
Homer is a couch potato and he drinks too much.
It describes a finished action at a present or recent time.
HAVE/HAS + PAST PARTICIPLE
Homer has realised he hasn't drunk anything for the last few seconds.