Read the Sudoku help page for the rules, and the techniques potentially required to solve BrainBashers Sudoku.
Intersections is one of the basic techniques people use when solving Sudoku.
Looking at Block5, where can the <7> go? The intersections of R5 & R6 limit the <7> to R4C4.
Looking at Block4. where can the <8> go? The intersections of R6, C2 & C3 limit the <8> to R4C1.