Hello people,
I had this game for free right now.
It is on my account but there is no "Install" or "Download" link.
How do I get the game on my computer?
It's the first time I use this website. Thanks

Assuming you're NOT using GOG Galaxy (I don't use it myself so I'm unfamiliar with how it works):
1) Using a web browser, go to this webpage and login to your GOG account: https://www.gog.com/account
2) Click on the game listed under "My Collection"
3.1) Click on blue "Download and Install Now" button if you want to install and run the game through GOG Galaxy
3.2) Click on the "Offline Backup Game Installers" if you want to install and run the game standalone without GOG Galaxy (you'll have to download all five separately).

Thanks brother! It's a hardest way. Steam is easier. Thanks for replying me

You can also use Galaxy if you like. It works a bit like the Steam client, they say.