Rides: Hard or Easy?
How to pick a club ride.
Speed, distance, and elevation.
There are a few basic things that make a ride "harder" or "easier": (1) the speed you ride at; (2) the distance you ride; (3) how hilly or flat the ride is (also called "elevation gain"); and (4) the surface you are riding on (paved, unpaved, trail).
BTCNJ categorizes road rides (paved) using a letter (A, B, C, D, etc) to indicate the general speed. Mountain and gravel bike rides (on unpaved paths or trails) are categorized similarly. The "terrain" (how hilly the ride is) is also indicated.
Some experience is usually required to really understand how this works.
If you are new, pick a ride that you expect to be fairly easy (and on the short side). If it's easier than you like, it's simple enough to pick a harder ride the next time. (Starting out with a ride that is too hard will likely be frustrating to you and the other riders in the group.)
Keep in mind that you are riding with a group (not merely in a group). That means it's important to pick a level that is appropriate (for you and the other participants).