The meaning of the preposition de changes with context to mean either of, from, by, with or about.
of ➜ É de madeira. (It's made of wood.)
from ➜ De onde você é? (from where are you?)
by ➜ Vamos de carro. (Let's go by car.)
with ➜ Estou de relógio. (I have a watch.)
about ➜ De que você quer falar? (What do you want to talk about?)
When the (preposition) de appears right before a verb in it’s infinitive form (with the ar, er, ir ending) this translates as: to talk, to do, to run etc.
Notice that you wouldn’t insert a de when saying something like, eu vou fazer or, vamos falar BUT YOU COULD!
In other words, if you were to say: vamos de falar em Português you’d be perfectly understood. In fact – this is how things are spoken in the Português of portugal.
The preposition de is most famously found (almost) always after the verbs GOSTAR and PRECISAR. So you’re really saying for example that you like of something or, need of something.
de fazer ➜ Eu tenho o direito de fazer. ➜ I have the right to do (it).
de falar ➜ Estou com medo de falar. ➜ I'm afraid to speak.
de comer ➜ É a hora de comer. ➜ It's time to eat.