Normal sudoku rules apply. Numbers on the outside of the grid give the sum of all the digits between the 1 and 9 in that row or column. Sandwich clues with the slash represent "or". So a 5/10 clue would mean the sum is either 5 or 10. The 39-arrow represents the sum of the digits along the indicated diagonal. The "x+1" in r5c4 means that the digit equal to "x+1" must be entered in that cell.