Medium puzzles ask you to track more possibilities before the next placement becomes clear. Use the notes button when scanning alone stops revealing a number.
Players who know the rules and want to move beyond straightforward scanning.
After marking candidates, inspect one row, column or box at a time. Even when a cell has several candidates, a digit that appears in only one cell of a unit must go there; this is a hidden single.
On a keyboard, use the arrow keys to move between cells and N to toggle notes. Read the beginner guide or try a worked naked-single example.