It varies from person to person. Some aces don’t experience sexual stimulation at all, some do. Some enjoy it, some don’t. It just depends on the person.
Here are some resources for writing ace characters, though if they can help at all:
Writing Demisexual Character (Without Invalidating Asexuality)
Stereotypes to Avoid When Writing Asexual Characters
Character Development Questions
Words and Concepts Used in Asexual Communities
Why So Many Stories About Asexuality Hurt Asexual People
How To Show That A Character Is Asexual
Negative Responses Asexual Characters May Get When Coming Out
Potential Sources of Conflict For Asexual Characters
Sex Scenes With Asexual Characters
Lithromantic/Akoiromantic Story Prompts
Relationships I Want To See More of in Fiction