Later is an adverb. It’s used to express time, either in the future or after the time you have mentioned.

For example: “I’ll see you later on Sunday.”

Latter is an adjectiv, which means near or towards the end of something

For example: “The English test had two parts: grammar and listening. I got tired during the latter part .”

!Latter can also be used to describe the second thing of two things mentioned.

For example: Later, at the end of his apprenticeship, he was offered the choice of going to Russia for further experience in the flax trade or of entering a university he decided on the latter course and entered the University of Edinburgh in 1882 to study for the B.Sc. Degree in Physical Science.