A great place to start is the mini painting starter sets by Reaper:

https://www.amazon.com/Reaper-Miniatures-08906-Learn-Paint/dp/B00NTMC49G

https://www.amazon.com/dp/B01N458GBK/

They're not too expensive, and they are a great intro to mini painting. They also come with pieces to practice techniques on, and a lot of paints to work with as well. I'd get those, and maybe some brushes.

I also would recommend a wet palette to keep paints wet between painting sessions, magnifying glasses to help see, and a mini holder.

I also got these brushes, which seem to be working well for me, and have a mix of useful ones.