learn the rule
literally
literally is an adverb. In its original sense, it means "in a literal or strict sense", as opposed to figuratively.
- The bookshelf is literally full of books.
- I literally ran to the shop. (Used my legs. Faster than walking.)
In modern usage, literally is also used as an intensifier, often where the meaning is plainly figurative.
- I literally died of embarrassment. (Did not actually die.)
- That was literally the funniest thing ever. (Probably wasn't.)
The intensifier use has been around since the 18th century. Dickens used it. So did Mark Twain. The Oxford English Dictionary now recognises both senses. Plenty of dictionaries do.
Pedants will tell you the intensifier use is wrong. Linguistically, it isn't. Whether you use it that way is a style choice, but be aware that some readers will twitch.
People who say "you're using it wrong" are technically wrong themselves. But people who say "I literally died" when they didn't are also slightly stupid. Everyone loses.
In formal writing, stick to the literal sense. In casual writing, the intensifier is fine but easy to overuse. If you can replace it with "really" or just delete it, consider doing so.
If you say "literally" five times in a sentence, you are literally annoying. And ugly.