Hyphenation can be tricky, but a general rule is if a compound adjective, which is made up of two or more adjectives that describes a noun, comes before a noun, it is normally hyphenated. For example:

A black-and-white dog.

A five-year-old tortoise.

If it is after the noun, it normally isn’t hyphenated.

The dog is black and white.

The tortoise is five years old.

However, there are always exceptions and it’s always best to double check if unsure.