Implement taskbox on frontend for user to complete, for quantative usability testing

I'm doing unmoderated usability testing on a website, and need to give visitors tasks to complete on the website, but dont know where to start, and hope to get advice from you. Maybe you know of a plugin, a link to a guide, or just which steps to take (just help me in the right direction) im quite familiar (not a pro) with html, css, js and php.

I wish to implement a box in the top left corner, that displays "task 1 - do this", once the user completes the task, task 2 will show up instead. The taskbox has to work across the whole site, so it shouldn't reset or disappear after page change.

crossing fingers for tips