"My grandfather is funny."
Translation:Mi abuelo es divertido.
If you're thinking of the "personal a," it's only used before direct objects. Here "my grandfather" is the subject.
I admire my grandfather. (Yo) Admiro a mi abuelo. (direct object)
You'll also see "a mi abuelo" used in sentences where it clarifies the indirect object: A mi abuelo le gusta correr. My grandfather likes to run. (Running is pleasing to my grandfather.)
Thank you, marcy65brown. That explains it well, and should be easy to remember.
Mi abuelo es divertido: my grandfather is funny. How would I say my grandfather is fun (as in My grandfather is fun to be with, but not necessarily a funny man?)