When you clone a remote repository, by default your local working directory will be on the remote repository's default branch. For a long time this was the master branch, but GitHub has recently started using the name main instead of master.
It sounds like your repository may have been created someplace else and then pushed to GitHub. Regardless of how you arrived at this situation, you have two branches named main and master, and it sounds like main is the default branch.
After cloning the repository, you will be on the main branch. You can switch to the master branch by running:
git switch master
Or:
git checkout master
The git switch syntax is newer. The two commands are largely equivalent (git checkout does more than git switch).
You can change the default branch of your GitHub repository by going to your repository settings. Clicking on "Branches" along the left. This will take you to the branch settings, where the first section is the "Default branch" section.
Click on the icon with two arrows, then select master as your default branch.
In the future, git clone will result in a working directory that is on the master branch.