A Warhammer 40,000 battle is unlike other games such as chess or draughts where you only move a single piece at a time. A tremendous amount of action takes place in a battle: squads manoeuvre and fire, tanks rumble into action and artillery fire roars down from overhead in a torrential downpour of destruction.
In a real battle this all happens at once amidst the confusion and chaos of combat. A Warhammer 40,000 game represents the whole ebb and flow of battle but in order to determine its outcome players alternate taking turns moving and fighting with their troops. So in a battle player A will move and fight with his forces first, then player B will move and fight, and then player A will move and fight again and so on.
During his turn the player can move and fight with all of his troops if he wishes. For convenience the actions of moving, shooting and fighting are dealt with one after the other. This means you move any troops and vehicles you want to first, and then you shoot with anyone who can and so on. This process helps everyone to keep track of what is going on and makes it easier to know when one player's actions are over and their opponent can start taking his turn.
In a complete turn each player performs their actions in the appropriate phases – the move, shoot and close assault phases to be precise. Exactly what happens in each phase is described in the turn sequence (opposite).