Can I make existing HTML template to a WordPress theme

[moderator note: topic title de-capped]

Hi All,
I’m sort of new to Wordpess and Ive been doing most of my site just using HTML. I recently started using WordPress because Its is a very easier way to keeping my site maintain. My question is can I make a custom theme using an HTML template by uploading the template into WordPress? I notice WordPress is writing in PHP so I didn’t now if this was possible….Thanks in advance!