I made a login form with HTml, but I don't know how to sign up and put it in db.

Now, you have to create a function to sign up and put it into the DB in a language like PHP

Usually there are many things like python, ruby, node.js, but the learning curve has the lowest php and is easy to access, so I recommend studying with PHP.

Now you need to install mysql or mariadb on your computer because you need to have a database in order to put it into the DB

I don't know if you just opened HTML or ran it as a web server, but you also need a web server like Apache or NGINX to print out the php interpretation.

In the case of Windows, if you install WAMP, all three are installed at once, and in the case of Linux, you need to install one by one (changed from apt-get to apt)

I recommend you to read the PHP course on the life coding website

https://opentutorials.org/course/478