Last year the free version only allowed for one grid with multiple topics. This year you can create as many grids as you would like with as many topics as you want under those grids.
If you have never used Flipgrid, it is a video discussion platform where student's can video booktalks, reflections, practice speaking in a foreign language,and much more. Student's can access via their computer or the app on their phones. Take a look at this video to get started.