Welcome to the wonderful adventure that is Backpacking! I am sure your local REI would have some in person (or currently "Zoom" type classes), but you can do a quick google search on what to be prepared for. See below for a couple of links:
As far as hikes in the DC area, I have been to McAfee Knob....it's a great little area with some breathtaking views. Several overnighters in that area.
A few questions I have for you though...do you already have your Big 3 (Tent, Sleeping Bag, Backpack)? Do you have a cook system? What time of year are you looking to go (your Big 3 could turn into a Big 4 or 5 depending on the season)?
one or more gifts or other benefits from the co-op.