We have created four scenario types for Warhammer 40,000: Standard Missions, Battles, Raids and Breakthroughs. Each of these scenario types breaks down into a number of different missions: five in the case of the Standard Missions and three for all of the others. For example, the Battles scenario includes a Take and Hold mission, a Meat Grinder mission and a Bunker Assault mission. To start with we'd advise sticking to the Standard Missions. This is because the Battle, Raid and Breakthrough scenarios are quite challenging even for experienced gamers and introduce extra rules to cover things like fortifications and preliminary bombardments.
The scenario to be played is chosen beforehand by mutual agreement, as is who will be the attacker and who will be the defender where this is appropriate for the scenario (this only applies to Battles, Raids and Breakthroughs). If you cannot agree on what scenario to play, or who will be the attacker and defender, then roll a dice for it, toss a coin, arm wrestle or whatever. Alternatively, you can use our cunning strategy rating system ...