I've been learning spanish for almost a year and I have just noticed the preposition "de". I find it hard to know when to use de in spanish sentences.
Any help would be great thanks!

Are you talking about in general or when used in prepositional phrases or with certain words?

I was thinking in general, but how are the other ways you can use it?
Thanks

In general, think of DE as meaning FROM or OF.

Soy DE los Estados Unidos- I am FROM the United States.

Possession-

Es la casa de Juan- It is Juan's house (the house OF Juan).

Certain Verbs-

This is the tough one. Prepositions will not always translate literally from English to Spanish. This may account for the reason why you have seen uses of DE that seemed out of place.

For example, in Spanish they dream "with" someone or something, not "of", as we would say in English. Suelo soñar con mi abuelito- I usually dream of my grandfather.

Enamorarse de- To fall in love with

Notice they use OF and not WITH (which would have been con)

Me enamoré de ella- I fell in love with her.

Despedirse de- to say goodbye to

Nos despedimos de Juan- We said goodbye to Juan

It is easiest to learn these verbs with the DE attached so you will remember to use it in sentences.

There are nouns that will also use DE where OF or FROM would not quite fit in English: La oportunidad de conocer al rey- The opportunity to meet the king.

I hope this was some help.