Read the Sudoku help page for the rules, and the techniques potentially required to solve BrainBashers Sudoku.
Swordfish is another advanced technique which can eliminate certain candidates from squares. We are looking for three rows (or columns) that contain up to three of a particular digit in the same relative position. Although Swordfish are an extension of X-Wings, not all of the squares have to contain the digit in question.
Using 'Show squares with a...' and selecting <8>, we can see that R3, R5 & R7 contain up to three lots of <8> in the same relative position. So the <8> might be in R3C7, R5C8 & R7C3 or R3C8, R5C3 & R7C7 or some other combination. Although we don't know which way around <8> goes, we do know that all other <8> from C3 can be removed because the <8> is in either R5C3 or R7C3. Similarly, all other <8> from C7 and C8 can be removed.