Ah, yes, it isn't very clear and really did need a tutorial (sorry!)
The idea is to make patterns from your collection (shown on the right panel), in the grid by swapping tiles (and later other actions too). To swap tiles you click twice on different tiles on the grid. You can see how many patterns and points you've made by hovering over the grid or progress bar. Then you submit by clicking the tick. The aim is to burn the progress bar down to zero within 3 submits. Then you get to choose an additional pattern, action or bonus and try again with a larger target.
But agree this isn't obvious, tutorial needed!