I also do not know hot to directly reply, but @Mbarreiro0711 I have had this happen a few times this cycle. I would take it as a positive sign that they are interested in whatever was said in the email you sent. In my experience, professors have asked to expand or initially state what my potential dissertation topic will be. I would ask what kind of advisor they are and/or how many students they currently are working with. The relationship that the department has with other departments, you would be surprised they do not all have established working relationships. The topic of funding comes in usually combined with if you are coming in with a B.A. or an M.A. I did make sure to ask, if it is not listed on their website, how many of their graduates are finding jobs afterwards and is there support in that process.