new to use redhat , want to install package

Hi All,

I don't use linux for a few years , I am really ignorance and outdated .

I have downloaded redhat 9 enterprise and installed it , when I use yum install , it pops

Code:This system is not registered with an entitlement server. You can use subscription-manager to register.
error there are no enabled repositories in /etc/yum.repos.d#yum -install httpd
Code:updating subscription management repositories
unable to read consumer identityI go to redhat.com and registered a account

1) redhat 9 is free , I can use it ? as I use centos before .
2) just want to install package to it , yum is good choice ?
3) what I need to do now is use the registered account in the linux OS ?

is there any url is a easy guide for me to follow to initial setup the linux

Thanks in advance