How to take care of a 15 year old dog?

I’m looking for some advice because I’m a little new to this situation.

My grandma recently left us with her dog, and he’s about 15 years old. We love him and want to give him the best life possible, especially now that he’s a senior.

He’s slower than before, sleeps a lot, and sometimes seems a little confused. We try to be gentle and patient, but I’m not sure if we’re doing everything right.

What are the most important things to focus on when caring for an older dog? And how can I tell if he’s comfortable and happy at this age?

Thanks so much for any tips or experiences you can share.