What's the first thing that comes to your mind when I say make up? 
Well, this can have several meanings. Let me explain.

Makeup is used as a noun while talking about beauty and grooming. For example, I really like your makeup today. (There is no gap between the words, or is sometimes used with a hypen)

Make up can be used as a phrasal verb in a situation where you've hurt someone and want to make things alright with them. (Also see my column Phrasal verbs on Friendships)
For example, I missed my son's annual day celebration so I am taking him to the park to make it up to him. 

Another use of this is when some damage has been caused and you're asked to pay something as a fine or compensation to make things even.
Eg: He was asked to pay a sum of $4000 to make up for the loss caused to the library.

Hope you learnt something new! Check out my new lesson where I assign you a little task to practice English and give you feedback on your work!