I take it you have NOT read the install instructions .
is the httpd set for the authentication type you are using ?
and is mysql or MariaDB set for this authentication
have you edited your config files to match YOUR SET UP !!!!
This is why i RECOMMEND that for the first 12 or so installs of the "lamp" stack
you build and MANUALLY install everything !!!!
then and only then save 30 minutes on the install and use the rpm's or deb's
setting up and CONFIGURING everything is VERY COMPLEX
not hard but COMPLEX
setting up a SECURE install of Apache
setting up the tables in the database -- while not hard can be a bit complex
adding the web based GUI "PhpMyAdmin "
IS RATHER COMPLEX if you want it SECURE
also all the other ancillary tools like
imagemagick ( if adding things that use images like " Gallery2")
all this makes for a bit of a "Gordian's knot" of complexity
none of it is hard to do
you just NEED to study like you would for taking a collage final exam