To start with you will just need to wear something that allows for easy movement with supple shoes that aren't too grippy.
When you can, you'll want to add a fencing mask, gloves, a training sword, padded jacket and so on. Some people do this quickly, most build it up to match the available funds. But more kit allows for more types of training.
No amount of protection can substitute the proper attitude towards training though. Care should always be taken to ensure your own safety, that of your training partner as well as to anybody nearby.
These suppliers are just some of the growing number that are supporting the growing HEMA market, they represent the ones that we use most.