Note that both disc and digital purchases require a download and install nowadays. The discs are basically just a way to prove you own the game.

If it's a digital purchase, you should be able to install it via the dashboard. It's been a while since I used my PS4, but I think when you first turn it on, there should be a row of apps you can scroll through horizontally, and FC26 should be one of them. If you highlight it, you should be able to press the Options button to get a list of actions, one of which should be "Install".

If it's on a disc, the above will still work, but the system should have tried to install the game automatically when you put the disc in. If it wasn't able to do that, it might mean there's not enough room, so you might need to delete a game or three to create more space.