When do i use-
trinkt
trinks
trinken
in german.

i don't understand when to use each word.

So if I'm correct on this
Trinkt is to say someone or somrething is drinking
Trinken is to say a group of people including yourself is drinking
Trinkst is to say you are drinking something. 

So it depends on who you are talking about. I hoped this helped.

The infinitive is Trinken
Drink
So the infinitive is Trinken
Ich trink
Du trinkst
Er/sie/es Trinkt
Wir Trinken
Ihr trinkt
Sie, sie Trinken

So if you want to say he/she/it drinks you say ' er/sie/es trinkt'

(You never use trinks)