Ok, first the very basic structure of a sentence:
Subject - Verb - Object.
First, we need a verb:
ficken (to fuck)
that's the infinitive. The stem is "fick-". The suffix "-en" is the sign for infinitive.
So we want to make a sentence in the present. The present endings are:
SINGULAR:
-e
-st
-t
PLURAL:
-en
-t
-en
Now the subject:
Like in most/all(?) languages, Subject stands in the case NOMINATIV. Our subject will be male, singular (and nominativ of course):
Der Mann (the man)
"Der" is the male article for the case NOMINATIV. In english, there's "the" for all 3 genera, in german and other european languages, there are 3 different articles.
And the object
Casus depends on the verb. the verb "ficken" wants to have the casus AKKUSATIV. In german, akkusativ-words look like nominativ-words. The only possibility to distinguish is the article. Our object will be male, singular, akkusativ:
Den Kellner (the waiter)
"Den" is the male article in akkusative.
So when you go like Subject - Verb - Object, you get:
Der Mann fickt den Kellner.