From the bottom of the app, at the far right there are 3 horizontal lines, that will be your Menu icon, from there you can look at tag explorer and topic planner on a general channel level.
To see how your tags rank on an individual level, you tap on one of the videos, tapping the description is the easiest, and from there, at the bottom of the page you'll see "best" is already selected, but there's 4 icons at the bottom, you want the second icon which looks like a shopping tag, that will show you how your tags on an individual level rank and from there you can select explore, or suggest, suggest will give you a range of suggestions, and you can type them into explore, and then explore and it will show you how well that keyword might perform on a search volume, competition, and overall score level.