@mctwist It’s OK, don’t worry about making it perfect. You’ll get better with time (he says from experience, hoping…) :)
PS. Here’s a good page of examples. There’s a link to step-by-step instructions at the end of that page too: https://www.sc.edu/about/offices_and_divisions/digital-accessibility/guides_tutorials/alternative_text/step-by-step-instructions-alt-text/alt-text-examples/index.php