As John mentions, the best way to prepare for the AD01 certification is to use Blue Prism's training materials. However, if you're looking to practice Blue Prism for a while, I'd say YouTube is good place to start. Personally, I think seeing someone use Blue Prism and you follow along is a good way to get a jumpstart and then to follow that up with all of the training documents Blue Prism provides.
The Developer Certification guide will give you the exact names of the documents you can search for on the Documents section of the Portal. If this is still confusing, please respond again and ask here. I think we forget how unintuitive Blue Prism's approach is to training. (I'm not complaining. It doesn't bother me but I get that reaction from people pretty frequently when I explain the structure of resources for Blue Prism training.)
Dave Morris, 3Ci at Southern Company