Weaving is making fabric from yarn, by crossing warp threads perpendicularly with weft threads.
The most basic weave, plain weave, is just the over-one-under-one weave, which makes a very practical, stable cloth. There are many other structures possible, though, formed by threadings on the loom, or by hand-manipulation of some threads.
Here's a picture of me sitting at the loom I use. It's in the process of being
threaded or "dressed" in this photo.
The loom model is called the "Mighty Wolf". It is a folding floor model which weaves up to 36" wide fabric. It's a great multipurpose loom, though it is too light to make rugs on. It has 8 shafts which means that one can lift 8 sets of threads separately or in combinations. That's 254 different combinations, plus they can be threaded in many orders, so it's a lot of territory to explore and use. And then there's different yarn sizes, colors, textures and fibers...
A list of loom makers can be found here.
Some weaving can be done using 'off-loom' techniques, including backstrap weaving which is traditional in the Andes, or card (tablet) weaving.