The sooner you learn how to belay (and feel comfortable doing it) the better your climbing experience will be. There are different types of belay devices and different types of belay techniques. Lots of gyms offer classes which is a great way to learn in a safe environment. Please be aware that improper belay technique can have life threatening consequences. Below, I’ve listed links to the most common aspects of belaying.
Figure 8 Knot (Note: the second knot is generally not required anymore at this point in time. In can be useful however to getting excess rope out of the way.)
ATC (Top rope) (This video shows top-rope belaying with an ATC device. ATC can be used in lead climbing but the technique is different. Please see link below.)
GriGri (Lead) (Note: A GriGri can also be used in top-rope settings.)
There are other techniques you can use, but be aware that these are the most recommended. Quick shout out to Matthew G. for requesting this post! Be safe and have fun!