Now the forces! Both are platoons out scouting. They just happened to run into each other and the fight is on!
Basic rules.
There are movement, shooting, and assault phases.
Infantry, unless otherwise noted, move 6" and may be slowed if in woods or bushes I'll describe the vehicle when I get to it
shooting. Models that aren't in close combat and can see a target in range may shoot at them, as described in their entry
assault If you haven't shot at anybody this turn you can move 6" (slowed as normal by woods or bushes) as a "charge" into an enemy unit. They then smack each other around turn after turn until one unit or the other dies or flees.
Be aware that in warhammer sometimes units will get scared and run away or do other things units under fire are known for doing. Guard are much more prone to this than marines.
The space marines have a small but strong force.
7x Assault Marines(total). Seargent with terminator honors and power sword, 2x models with plasma pistols.
These guys have jump packs. So they can walk as normal troops if they want, i.e. 6", or they can "jump" 12" in the movement phase. This isn't slowed by woods or anyting. But if you try landing in bushes or woods you might crash.
They have pistols instead of rifles, so they can shoot AND assault in the same turn. But they can only shoot 12" Don't worry about the upgrades so much, it just makes them better.
These guys love close combat. You'll want to get them charging into IG units who they will then rip to shreds with their chainswords.
Next some regular space marines in an armor transport
8x regular marines. One has a flamer, one is a seargent with a power sword
These guys like close combat too but they're more about shooting with their rifles (bolters).
If they say still they can shoot 24" with bolters or if they moved they can shoot TWICE with the bolters up to 12"
The flamer only reaches 8" but at close range can make many guardsmen into crispy critters!
And their rhino transport(which they start the game in, unless you don't want them too)
A lightly armored transport for the marines.
It can move 12" every turn and drop the marines off. If it moved they can't assault that turn, but they can still shoot the heck out of somebody!
It's got rought terrain modifications, so if it moves less than 6" it has a much better chance to safely go through woods, it would also be able to shoot the machinegun on top.
It also can fire smoke launchers once in the game. This means it can't shoot, but makes it more survivable against incoming fire! Very popular when trying to get across the map while under fire!