The brew pot (kettle) is used primarily with brewing, but can also be used in mead making.
I use a 4 gal. Stainless Steel stockpot for making 5 gal batches of beer. This means I end up with a 3 gal. concentrated wort that has to be diluted with water to get my final volume.
A larger kettle would be better, but this is cheaper and still produces good beer. If you are working on a tight budget, this is the way to go/start. Later you choose to step up in size. Some home brewers actually use 55 gal. Stainless drums in their systems. Maybe this will be you in a few years.
Stainless Steel is usually the metal of choice, but aluminum and copper can also be used. Countless debates have taken place about the use of aluminum, and as far as I can tell there is nothing wrong with this choice. Just make sure it is heavy duty construction, and avoid the use of caustic clensers.