@patricialamas congratulations!
What @Nyrryl-Cadiz and @PenAndrew said: communicate and ask questions. Be upfront with them and let them know that this is your first time working with a design agency. If they know you're a newbie, then they'll be able to help you out. Acting like you know what you're doing when you don't is often obvious -- they'll see right through that. You'll come across as more professional if you're honest and ask questions. It will tell them that you're taking this seriously and want to make sure that you do a good job and will try your best to deliver exactly what they're looking for.