Example : Ella trae la tarta para tu fiesta de cumpleaños. She's bringing the cake for your birthday party.

Hola Susan

This is a specific use of the present in Spanish (trae) to express something that is "going to happen" that doesn't sound quite right in English if we used the present tense. We can say "ella trae" meaning in English "she is bringing" (future) but cannot use "está trayendo" because that would mean in Spanish that she is doing the action at the moment of speaking, but this is not what we mean; we mean the future "she is bringing..." 

I hope this clarified it.

Saludos

Inma