The purpose of Squaro: finding rounds to complete.
For that there are in each box a number from 0 to 4, which corresponds to the number of rounds to complete among those at the four corners of this box.

All grids have a unique solution. 

Instructions:
-- General --
Cross: OK
Triangle: Back
Select: Change language

-- Selection grid --
Start: Starting grid
L and R: Switch between levels

-- Basics --
D-Pad: Move
Cross: Fill / Empty circle
Triangle: Return to selection grid
Start: following grid once the grid current completed