Welcome to the community! It is great that you are reaching out in efforts of showing love and support of somebody you care about.
We like VineMaple's advice!
Having come out to our closest friends about our regression, all we sought of them was their acceptance. We did not seek their involvement in our Littlespace since we understood that not everybody identifies with any role in this particular community. Being a Caregiver or Little are very much personality types, and it is okay not to identify as either!
Our first suggestion is to allow your friend to express their thoughts and feelings. It is amazing that they came out to you, as it is a special and intimate revelation. It would be great of you to give them the space for them to express themselves from a mature context, but that doesn't mean you to need to participate with them in doing anything differently aside from general acceptance.
Do understand that just because they came out to you does not in any way that you should be placed in the position of their X (where X is Caregiver, Littlesitter, Mommy, Daddy, etc.). Do not feel compelled to all-of-the-sudden step in for them as what role you feel they need. That isn't why someone comes out to someone else. They are just seeking your acceptance and understanding, not participation or active involvement.
We do not at all recommend that you become their caregiver in efforts to please them and make them happy. You can show them great acceptance without attaching yourself into a deeper connection. Being somebody's caregiver implies a higher sense of responsibility and commitment, akin to a committed relationship (a step higher than dating). So, if you learn and explore the lifestyle with them as their caregiver then you run the risk of establishing some dependency, and going back to friendship then becomes hairy situation.
However, if you have genuine interest in the community, we heavily suggest you educate yourself separately. This website has amazing articles that should point you in the right direction!