Hi and welcome!
In Arch based distros like Endeavour we use the Arch repository’s using terminal. There are the official Arch “repo”, and the AUR (Arch User’s Repository).
The ordinary Arch repo can be found and searched (under Package search) here:
The AUR can be found and searched here:
The command to install a package in terminal is:
sudo pacman -S “package name”
The command to install from AUR (and the ordinary repo) is:
yay -S “package name”
Then you’ll be prompted to type in your password, and the package will install. In yay there are further steps, but generally hitting “enter” does the trick.
Don’t hesitate to ask if there’s something you’re wondering about. 
PS. Endeavour has an excellent wiki that you might consider reading. DS