You need to sign up for web space that provides you with FTP details.
They generally send you those details via email after you sign up, or they provide you with a user name and password to login into their web site and manage your web space; there you should find your FTP details.
Once you have the FTP details, you should download a program called Filezilla.
You can download Filezilla here: https://filezilla-project.org/
Once you install and open Filezilla, you can create a new connection to your web space by using the FTP details you have for your site. (There are plenty of youtube tutorials on how to use Filezilla)
Once connected, it's a case of dragging and dropping of the files from your computer onto the webspace.