Looking again at the sample puzzle, we see that the triplet to the right in row 1 must total 24. The only possible combination for 24 is always 789. So this means we can immediately rule out any 7, 8 or 9's from any other cell in the two other triplets of that row and also in the other cells in that block. Frame totals of 6, 7 and 23 also only ever have one combination of numbers. But for other numbers, as soon and they are reduced to only one possible combination, you can immediately rule out those numbers from other cells in the same domain.
This is more of an advanced technique and is only employed in the generation of hard puzzles.

At first you may find these Frame Sudoku puzzles difficult to solve, especially for the first few cells but practice will help you see the patterns more quickly. Remember to use the Solve One Cell feature which will show the steps to solve a cell.
Good luck.