Makeup and make-up are both correct, but mean completely different things. You apply makeup to your face. When you miss a test in school, you may have to do a make-up test. You use the hyphen here, because it is an adjectival figure of speech - it modifies "test." If it's not used as a modifier here, you drop the hyphen: " I have to make up the test." Finally, not to confuse you, if you create or invent something, you "made it up." For example: "I'm going to make up a sentence to explain the different uses of 'make up' to you." Online is correct NOW. Twenty years ago, when the Internet was new, the concept of "on-line" was fresh and new and the two words had yet to become a word. English is constantly changing, and so eventually "on-line" became an acceptable one-word idea, and the hyphen was dropped, leaving "online" as the word.

The tendency is to avoid using hyphens - people are often uncertain when to use them. I have seen both your examples but it is less common to see the hyphenated versions.