Xfinity Mobile and Xfinitywifi, what are they used for?

I am new to Xfinity and need some help understanding some options.  When my Xfinity internet was installed, the tech had me log into the service with my last name.  There are two other options listed, one called Xfinity mobile and the other called Xfinitywifi.  What do I use these two for or direct me to a link explaining them.