Actor is a gender-neutral term that can be used to refer to anyone who performs, regardless of their gender. It is the more inclusive term and is often preferred in modern usage. For example, the Screen Actors Guild (SAG) uses the term "actor" to refer to all of its members, regardless of gender.
Actress is a term specifically used to refer to a female performer. It is still in common use, but it is sometimes seen as outdated or sexist. Some actresses prefer to be referred to as "actors" instead.
The difference between "actor" and "actress" is similar to the difference between "man" and "woman." "Man" is the gender-neutral term that can be used to refer to anyone, while "woman" is the term specifically used to refer to a female person.
In conclusion, "actor" is the more inclusive term that can be used to refer to anyone who performs, while "actress" is the term specifically used to refer to a female performer.