Ah, claro. Creo que puedo ayudarte un poquito, pero in inglés para explicar, ok? No puedo hablar alemán; lo siento!
...
DE
De means "of". There are a few uses:
1. Origin - Being from a certain place.
-ex.
"¿De dónde eres?" "Yo soy de Alemania."
2. Characteristics - Used to describe the material an object is composed of and other inherent characteristics.
-ex.
Esta mesa es de madera. - This table is wooden./This table is made
of wood.
-ex.
Es una canción de cuatro minutos. - It is a four minute song.
-ex.
Una copa de agua. - A cup
of water.
3. Possession - Use it when you're talking about ownership.
- ex.
Esta casa es de Maria. - This is Maria's house.
**de + el = del
...
A
A generally means "to", but also has a lot of uses:
1. Destination - Moving towards a place or location.
-ex.
Yo voy a los Estados Unidos. - I'm going
to the United States.
-ex.
Tengo que ir al baño. - I need to go
to the bathroom.
2. Connecting verbs - Placed between a conjugated verb and an infinitive. Usually after verbs that describe the beginning of an action.
-ex.
Ella va a bailar pronto. - She is going
to dance soon.
-ex.
Empecé a correr. - I began
to run.
3. Time - Used to describe specific times.
-ex.
El tren sale a las 7. - The train leaves
at 7:00.
-ex.
La reunión comienza al mediodía. - The meeting begins
at noon.
4. Indirect Object - Used before the indirect object in a sentence.
- ex.
Le doy un libro a Eva. - I give the book
to Eva.
**a + el = al
...
EN
En usually means "in" or "on".
1. Location - Used for the physical location of an object.
-ex.
El gato está en la mesa. - The cat is
on the table.
-ex.
Las joyas son en la caja. - The jewels are
in/inside of the safe.
En is also used with many verbs and to create many idioms. For example:
- en caso de... - in case of...
- en lugar de/in vez de... - instead of...
- pensar en... - to think about...
- insistir en... - to insist on...
- En serio! - Seriously!
...Pues, no es una lista completa, y no sé si es clara.