In Portuguese we have a distinction. Antes de is a preposition, antes que is a conjunction and antes is an adverb. In English there is no difference between the preposition, the conjuntion and the adverb. It is always before.
antes que conjunction (before)
Reserva-o antes que alguém o faça.*
Reseve it, before it is done by someone else.
antes de preposition (before)
Lavamos sempre as mãos antes de comer.
We always wash our hands before dinner.
antes adverb (before)
Não sei se devo fazê-lo antes.
I don't know if I should do it before.
* The conjuntivo, faça, is used, because it is unclear whether someone will do it, see chapter 12. If only the moment were insecure when someone will do it, we would use the conjuntivo do futuro.
Antes in all variations shouldn't be confused with ante. Ante is a preposition and can describe relationships in space, but can be used as well in a metaphorical sense.
ante relationships in space / metaphorical sense
Ficou parado ante a porta.
She stopped in front of the door.
Só há um modo de vencer a tentação, e é ceder ante ela.
The only way to get rid of a temptation is to yield to it.