These are a must if you're using drippy glazes, and are a good idea even if not.
Drip catchers are a small sacrificial disk that saves both your pot and shelf. Even if you're not using drippy glazes they're worth using, they'll protect the shelf if the glaze crawls or flakes off the pot, and means if there is glaze residue on the shelf it doesn't contaminate the bottom of the pot.
They are essentially thrown as small plates, then the centre is opened all the way down to the batt and that clay is used to lift a raised ring for the pot to sit on. This gives the pot support but leaves the lip of the foot raised above the catcher part of the drip catcher. If the glaze runs it'll land on the catcher, but the gap means the two don't fuse together if it does (usually, in cases like the mug above then there's no hope). A taller drip catcher will be safer at the expense of kiln space.
I throw mine in the same clay as the pieces, that way there's no contamination between them. In my experience, using a darker clay for the catcher will transfer some of the iron burn colour to a lighter pot. I use between 100-300g depending on the size I want. This video shows around 200g thrown to 15cm, which would be about right for a soup bowl or giant mug. They take me about a minute to throw and I don't bother trimming them.
I genuinely can't recommend them highly enough. They've saved my shelves on so many occasions, and they're so fast to throw and use so little clay that they'll earn their keep on the very first time they're needed.
That's all there is to it! Please try it and let me know how you get on, message me or use the hashtag oldforgecreations (I often miss @mentions on Instagram and there's no way to find them afterwards, but I'll see the tag). Good luck!