How to create.htpasswd popup in free host website?

Is this possible and if it is, how?
Thanks for your answers.
(I want to lock a folder)

Yes, it is possible. You can use these generators for this:

http://www.htaccesstools.com/htpasswd-generator/
http://www.htaccesstools.com/htaccess-authentication/

and then put the generated lines inside respectively new .htpasswd and .htaccess files on the htdocs folder with a File Manager.

What’s the path of the htdocs folder?
(I’m really sorry for not knowing, but I’m pretty new…)

You can just consider the htdocs folder to be the root of the domain name files, instead of also knowing the path of the htdocs folder.