You’re welcome. Enjoy your mirror

get them to fade after 5 seconds.

The updateInterval: 5000, is in milliseconds, so 5000 = 5 seconds. You change that to set the time that a new compliment appears

Can someone explain to me how I go about doing this?

The readme for the compliments module has all the information you need. I suggest you read it. With that, here is one way of adding compliments, in your config entry. However, this way can make your config cumbersome, but it does work. The readme explains how to use a remote file so you don’t fill up your config with compliments.
https://github.com/MichMich/MagicMirror/tree/develop/modules/default/compliments

And here is a config entry you can use. See how I added compliments to the file? Just follow that format and you’ll be fine.

		{
		module: "compliments",
		position: "lower_third",
			config: {
				updateInterval: 5000,
				fadeSpeed: 1000,
				compliments: {
		anytime: [
			"Hey there sexy!",
			"RTFM!",
			"The readme will help!",
			"Last one no comma"
		],
		morning: [
			"Good morning, handsome!",
			"Enjoy your day!",
			"How was your sleep?",
			"Last one no comma"
		],
		afternoon: [
			"Hello, beauty!",
			"You look sexy!",
			"Looking good today!",
			"Last one no comma"
		],
		evening: [
			"Wow, you look hot!",
			"You look nice!",
			"Hi, sexy!",
			"Add your own like this!",
			"Watch your formatting!",
			"Last one no comma"
		]
	}
}
},

You can copy and paste it and edit it if you like.

Then read the readme! ;-)