Sims 4 comes in different editions and depending on what you bought, you’ll get different extra content that you can unlock.
What content do you qualify for ?
You can check Origin what you’ll get
Click in My Game Library on the game and choose Extra Content
There are also some rewards for owning Sims 3 games (offer not valid anymore)
How do you get your content ?
The extra content either comes as content for the game or as a soundtrack, that you can download and play on your favorite device.
Different than Sims 3 there are no codes for the content. It’s unlocked the first time you start the game (this happens with each new installation.
So all you have to do is start the game and you’ll find it in your game.
You can find the soundtrack in Origin under Extra Content. Scroll down to the soundtrack and click on Play to be taken to the files directly and play them with a program of your choice.
You can also just copy the files to a place of you’re liking.