"I drink water."
Translation:Ich trinke Wasser.
The verb endings change depending on the person. There are some remnants of this in English - "I drink", but "he drinks" with an additional "s".
You take a verb like "trinken" (to drink) and get rid of the "-en": "trink-". Then you add the ending depending on which person you're talking about:
ich trink-e (I drink)
du trink-st (you [informal, singular] drink)
er/sie/es trink-t (he/she/it drinks)
wir trink-en (we drink)
ihr trink-t (you [informal plural] drink)
sie/Sie trink-en (they/you [formal singular + plural] drink)
It differs in the tense. "I drank water" is past tense. Since there are multiple tenses for the past in the German language, "I drank water" could be translated in various ways. The most common one would be "Ich habe Wasser getrunken" (present perfect). You could also say "Ich trank Wasser" (past tense) but using the past tense to state things that happened in the past is considered as an old-fashioned way to talk (you'd sound a bit like a person from medieval times when using the past tense).
"I drink water" is present tense. So if you say "I drink water" that could be referring to you drinking the water right now. "Ich trinke [Wasser]" (present tense) could also refer to a general habit [of drinking water]. So if you're asked what your favorite drink is and you normally drink water most of the time you could answer "Oh, ich trinke nur Wasser" which would translate to "Oh, I only drink water". So the present tense is not only used to refer to actions taking place whilst using it.