i am not able to understand when to use trinkt or trinke
It's simply verb conjugation. English has it, too.
In English, when we are talking about ourselves, we would say "I drink;" when we are talking about he/she/it, we would say "He/she/it drinks." The extra s is the product of conjugating the verb.
The same goes for German. For "I drink," the conjugation is trinke; for "He/she/it drinks," the sentence would be "Er/sie/es trinkt."
Most verbs follow that rule.