Commuting options from Madrid city center to Leganes campus

I am going to Universidad Carlos III de Madrid next semester for an exchange term from Canada. I will be studying at the Leganes campus for 4 months, and I am trying to determine whether I should find an apartment in Leganes so that I am within walking distance to campus, or get an apartment closer to the city center and just commute. I only have to be on campus 3 days a week, so I think I would prefer to be in the city center for most of my time as I would then be closer to the main train station and the airport, as well as more lively things like shops, bars, and restaurants.

But, I am having trouble understanding the commuting options from the Madrid city center to Leganes. I know Leganes station is in zone B1, and there is a 30-day youth public transit pass that allows unlimited interzonal travel for people under 26 (which applies to me) for a total of 20 euros per month. This option would be great for me, as it is within my budget and would allow me to get around to many different places in the city.

So my question is: what type of transit does this pass allow you to take? i.e. is it for the metro/subway, above-ground train, bus, or a combination? Additionally, how long would it take to get from somewhere in the city center to Leganes using this pass? And what would be the route? How often does this train/bus run? I cannot seem to find this information anywhere online, as the Spanish websites are a little bit confusing and I don't understand the different types of public transport or what is included with which passes.

Any information would be greatly appreciated!