Hi - I am a Grokker user who joined two and a half months ago. If your question refers to how to search for specific videos, I sympathize because at first I was confused, too. If you reached level 15 (congrats!), you probably know how to navigate pretty well and maybe are searching for a formal, printable guide for a friend. I don't think that exists, but here are three ideas:
(1) On the homepage, scroll down about midway/halfway down the screeen. You'll see a section called "Find Your Perfect Video", where you can use the prompts to specify the topic, level and time length you seek each day.
(2) A second way to find what you want is to click on yoga, fitness, cooking or mind at the top of the screen and then simply explore each sup-topic that piques your interest.
(3) A third way to get a sense of the breadth of Grokker's terrific offerings is to click on my profile (tlc tlc in the search bar at the top of the screen) and then click on my "collections". I chaptered all of Grokker's cooking, fitness and yoga videos, so you might get a sense of what is available in those three categories simply through a super-quick, 30-second scroll through my collection topics. (I didn't chapter Grokker's "mind" category because from my perspective Grokker chaptered that category really well, so there was no confusion on my part and no need for me to create collections. I also didn't include fitness videos from "Pace and Go" because rumor has it that "Pace and Go" will release new videos soon. I'll wait until those new videos are released before creating my very final collection.) Good luck! :)