Movement of the checkers
The most important rule in a backgammon game is that you have to move the checker(s) as many spaces as the sum of the dice (or four times the dice if you roll doubles) is equal to. If you can not make this move, then you need to move one chip as many spaces as the largest dice (or if you roll doubles, the largest multiplier of the dice) is equal to. This may sound easy to achieve, but it can be tricky.
Consider, for example, the case where you roll a 4 and a 3. Based on the above rule, you can either move one checker 7 spaces or one checker 4 spaces and another one 3 spaces. At the beginning of a game, you could easily follow this rule. But as the game progresses, and your opponent is blocking you, you may find yourself in the unfortunate situation to make a move that you do not want to. So, in our previous example, if all checkers could move 4 spaces, and there is only one checker that can move 4 and then 3 spaces, you have to move that checker. If you move any of the other checkers, you will violate this rule.
The iTavli game enforces this rule, as you can see in the screenshot. The player could move two checkers, but iTavli does not allow the player to move the selected checker. If the player had been able to move that checker, (s)he would not be able to play the first dice (i.e., 4). Thus, the player has to move one of the checkers that lie across the board from the selected checker.
The winner of a game is the one who first collects all the checkers from the collecting area. You can start collecting checkers when all the checkers are in the collecting area.
You roll the dices and you collect a checker that lies in the triangle that a dice points to. Note here, that each quarter has 6 triangles, and thus, the far most left triangle is numbered 1 and the far right triangle is numbered 6. If you roll a dice with a number larger that the number of the triangles that are occupied, you collect checkers from the triangle that is far most to the right. For example, if you have checkers in triangles 1,2, and 4 and you roll 5 and 2, then you collect one checker from the 2nd triangle and one checker from the 4th triangle.