Naked Pair. (row 2, left). A naked pair is made of two truths (blue) in two cells in row 2. They are covered by two row links (red) in the same row. All digit 3s and 7s in row 2 are eliminated.

Hidden Pair. (column 8, right). A hidden pair is made of two truths in column 8 for digits 4 and 9 (green). They are covered by two cell links (light blue). All digits in the two cells are eliminated.

X-Wing. (r69 c36). An X-Wing is made of two truths for the digit 8 in rows 6 and 9 (red). They are covered by two column links (light green) in columns 3 and 6. All digit 8s in columns 3 and 6 are eliminated.

3D View. When viewed in 3 dimensions, it's easy to see that the logic is the same in all three cases. Each forms a rank 0 loop with 2 truths and two cover links. The only difference is their orientation.