Jose1992 unfortunately guides can quickly get outdated during our beta phase if the authors don't keep up. It's advisable to make sure everything is up to date before following instructions.
If you are familiar with your hosting solution, you should find everything you need in our install guide https://flarum.org/docs/install.html
If you are trying to install on a shared hosting or VPS, make sure it meets Flarum requirements (in particular, SSH access and Composer).