Step-by-step explanation:
Akkusativ = wen oder was ("who" in English, a substantive that is being used or handled by another substantive).
Dativ = wem oder was ("whom" in English, direction, e.g. target of a movement or affection).
Genetiv = wessen ("whose" in English, possession).
Nominativ = wer ("who" in English, a substantive that is using or handling another substantive or is simply doing something).
1. Der Mann schreibt der Freundin eine Email. The man writes an email to the girl friend.
"der Freundin" Dativ
"eine Email" Akkusativ
"der Mann" Nominativ
2. Dr. Koenig gibt der Frau Tabletten. Dr. Koenig gives the woman pills.
"der Frau" Dativ
"Tabletten" Akkusativ
"Dr. Koenig" Nominativ
3. Wir zeigen den Gaesten das Haus. We show the house to the guests.
"den Gaesten" Dativ
"das Haus" Akkusativ
"Wir" Nominativ
4. Der Vater kauft dem Sohn einen Computer. The father buys a computer for the son.
"dem Sohn" Dativ
"einen Computer" Akkusativ
"Der Vater" Nominativ
5. Die Mutter schenkt der Tochter eine Puppe. The mother gives the daughter a doll as present.
"der Tochter" Dativ
"eine Puppe" Akkusativ
"Die Mutter" Nominativ
6. Ich verkaufe einem Freund ein Auto. I sell a car to a friend.
"einem Freund" Dativ
"ein Auto" Akkusativ
"Ich" Nominativ
7. Er serviert Freunden Kaffee. He serves coffee to friends.
"Freunden" Dativ
"Kaffee" Akkusativ
"Er" Nominativ
8. Sie kocht dem Kind (eine) Suppe. She makes soup for the child.
"dem Kind" Dativ
"Suppe" Akkusativ
"Sie" Nominativ