Need help with custom template

I am new to WordPress and am trying to create custom templates. I took my html and css pages, added the required php tags and saved them to wp-content/themes/default/. When I go to the dashboard, the template is not showing up as an option. I also downloaded and installed an existing template, but that doesn’t show up either. Am I missing a step? I’ve been trying to figure this out for hours now.

Thanks in advance for any help!