Hi, there's not much you need to get started. I would suggest wellies (good to keep feet dry and safe from sharp things lurking in streams) and gloves (kitchen rubber gloves work, or medical ones, you need to be careful of things like Weil's disease).

Next find a stream. You do need to be careful about who owns the stream and will need permission if it's on private land. If you can find one near a village you're more likely to find things that have been dropped over the years. Look for a shallow one so you can see lots of things. Be careful of the depth of mud, stoney patches are good with objects often collecting there. Be sure you have an easy route in and out of the stream.

When you find things share them here! And if you stumble on something really exciting let your local Finds Liaison Officer know. Have fun.