The practice mode is the standard round. Each series is classified in a tree of sections. You choose the section that you want to work with, the type of exercise that suits you and its difficulty.
Catogories: each category has an icon that sometimes describes the number of moves (x1, x2, x3, ...) and also the difficulty of the puzzles (shown with a green face (easy), orange (average), red (difficult). See the below example from the category of easy puzzles to solve in 3 moves.