First Step
bronze
Complete 1 level
Choose Play, then level 1 in the 4×4 section. Complete one grid for this trophy. I would switch to numbers with while learning the rules, using the numbered-display control on the right.
Select an empty cell, open its cat/number popup and choose the entry to place there. Keep the printed starting entries and fill the remaining cells. Use 1–4 once in every row, column and outlined 2×2 box.
Here is the completed first grid. Each line is one row, starting at the top:
3 4 1 2
1 2 4 3
2 1 3 4
4 3 2 1
Check the existing entries against this arrangement before filling the blanks. If you put a number in the wrong square, select it again and choose its replacement. Finish the grid and wait for the completion result before leaving. Then return to the level screen to check it has been marked complete.
External grid reference: 4×4, level 1 cat and number images (nana, Steam)