Are you saying it needs to pick 2 tiers of position, first which 3x3 grid then the block within it? That's not totally clear. Anyway, you would set a variable to floor(random(9)), which picks a random whole number from 0 - 8. Then you would spawn the player on the block where gridblock number = var. If you are choosing a 3x3 grid from the entire map before this then you would give each of the gridblock two variables, a main one where it decides which 3x3 block to go to initially and then use the floor random to pick 0-8 for individual block inside the grid. Something like grid 1, block 8 etc.