Hi Heidi,
Former customer, now Adobe Workfront employee here! As a customer, early on, a lot of our training materials were quick one-sheets created in Word with links and screenshots. As we solidified our processes, we created more in-depth guides (powerpoint guides that explained who, what, where, when, why, and how for each role).
As @Richard Leek‚ mentioned - the powerpoints are a great place to start! It gives you some basic framework that you can customize and build off of.
Another idea - for those that will be in the tool regularly (your planners and workers), you might think about setting up a training project. You can set up a practice/test portfolio and exclude those projects from your reporting - but you can assign tasks for things you want them to do, have them test proofs, tag other users, or even have a task for "Watch XYZ training video" with a link in the description.
I would recommend thinking about what your most common questions are. For me, it was around logging in, requesting access and proofing, so those were the first things we tackled. Even before they were formalized in a PDF, I had email templates of responses I sent to common questions. The more you can templatize things for yourself and create shortcuts to answers, it'll help you in the long run!
I don't have any of my old examples, but hopefully others can share some of theirs to give you some inspiration.
Welcome to the Adobe Workfront family!
Leslie