Hi, it depends on the verb you use (for example "sehen" is always with Akkusativ: Ich sehe den Vater. --> I see the father.). Some verbs want Akkusativ, it is always an object, not the subject. We have two questions for the Akkusativ: wen? (for persons) and was? (for things). The forms are:
maskulin: den, einen, keinen, meinen
feminin: die, eine, keine, meine
neutrum: das, ein, kein, mein
Plural: die, keine, meine
For example: Ich (subject) sehe (see) einen Mann, eine Frau, ein Kind und keine Hunde.
Other verbs, which want the Akkusativ: lesen, essen, trinken, kaufen (there are a lot of them, for this reason a good tipp is to learn always the verb and the Kasus)
:)