Order Campaign
Mission 1: No Retreat!
At thee start of the game there is a short intro. After the Intro the game starts and you have 5 squads of Imperial troops, commisar and command squad. First of all construct your max amount of tech engieers. Make 2 imperial squads capture the two command posts near the 2 gates. after capturing them build listing posts on them, and start build turrets around them, as there will be swarms of chaos troops pouring in every 2-3 minutes.
Mission 2: Hold the Line!
Mission 3: Between a Stone and an Axe
Mission 4: Final Journey
You can play this mission with either the Imperial Guard or the Eldar. You can switch sides anytime you want until one of the factions either wins or fails.
Imperial Guard
Your goal is to escort the Ultramarines' Land Raider from the bottom to the top and through the Psychic Shield. You can't control the Land Raider directly, but you can call it to your Command Squad (Sturnn to be specific) within a limited range. You need to use this ability to call it through the last gate. On the way you will be harassed by massive amounts of Chaos Space Marines and Orks spawning from the bottom edge. You can only build Listening Posts and Plasma Generators, but there are some structures you can commandeer to raise your Squad/Vehicle Cap.
There are basically two ways to do this: you can either dash for the top or hole up in your little base, defend against the waves there and prepare. When you move for the Psychic Shield, you can either let the Land Raider take its own path or open shortcut gates by capturing strategic points.
If you decide to strike for the Psychic Gate right away, I recommend letting the Land Raider go where it wants and supporting it with whatever infantry and vehicles you can scrape together. If you open the shortcuts, you need to divide your troops and the enemy will just follow you through. Don't try to assault the huge Chaos/Ork base at the bottom, you will die. The Ultramarines get replaced with drop pods if they die, but keep an Enginseer along to repair the Land Raider. Take over the small Imperial Guard base next to where you start (by moving your Command Squad to the Field Command), build a Listening Post and some Plasma Generators and start research/production there while directing all you can to protect the Land Raider. Don't worry about the base, it won't be attacked. Take your Command Squad north to commandeer an Infantry Command (a bit to the right from your base), a Mechanized Command (higher up near the left edge) and a Mars Pattern Command (near the upper edge, left from a Critical Point). Send one Guardsmen Squad along to capture the Relic near the Critical Point so you can build a Baneblade. Now run back and slow down the enemy waves with whatever works for you.
If you want to hole up for preparations and maybe some revenge, commandeer the starting base and keep the Land Raider around your Listening Post (by calling it with your Command Squad whenever it wants to leave) and support it with what it takes to blast the enemy waves. Start research/production and run your Command Squad up to commandeer the other structures again (you can dash up to the Mars Pattern Commmand and be back before the Land Raider decides to leave). Build the Baneblade and bring it down to your other troops. Now you can have maybe 4-5 squads of Karskins, Command Squad, the Land Raider & Ultramarines, 5 Leman Russ tanks and the Baneblade kick the crap out of that huge Chaos/Ork compound and take your time to the Psychic Gate.
When you get the Land Raider through (remember, you need to use the Command Squad) you win and the Eldar get wasted. You now get the Titan of the Emperor final mission.
Eldar
Mission 5a: Titan of the Emperor
You will get this mission if you win Final Journey with the Imperial Guard.
You will start with a base built on top of the Titan, surrounded with Strategic Points and Slag Deposits. Your goal is to build six Thermal Plasma Generators to power the Titan's weapons, which you will use to defend against the Necrons, who will attack when you have finished four of the generators. Meanwhile you will be harassed from Chaos Space Marine bases to your northwest and southeast and Ork bases to your northeast and southwest. To your south there is an Imperial Guard depot under siege by Orks where you can get a free Baneblade by repairing a damaged Mars Pattern Command.
Start by scattering your infantry and capturing the Relic and all Strategic Points as fast as you can. You should build Listening Posts quickly so you can tunnel-transport infantry around to answer the attacks; the nastier ones come from the Chaos Space Marines (NW and SE). You can safely build three Thermal Plasma Generators so you should have plenty of Power. Build more Heavy Bolter Turrets when you can. Start your research; a couple of Karskin squads will really help your defense. As for vehicles I skipped the weaker ones and went straight for Leman Russ tanks.
While you're scrambling to build up and defend your Strategic Points and generators, you also want to get the southern depot before the Orks overwhelm it. Also, the earlier you get the Baneblade the easier it will be for you. I had trouble detaching my light infantry from defending my base so just I broke through with my Command Squad, Chaplain and Space Marine Squad, tunnel-transported a Techpriest Enginseer over to repair the Mars Pattern Command and blasted the Orks with the Baneblade. After this, you can either pull back to your main base to defend and build your generators (after which the Necrons arrive and annihilate everything anyway) or, if you want to prepare in peace, take the Baneblade and some support troops and destroy the enemy camps.
When you have finished the Thermal Plasma Generators (just build the final three at the same time) the Titan's weapons are activated and Necrons attack from all directions. They will come with superior infantry and Monolith moving bases and totally kick your backside if you don't use the Titan. Hotkey the six Titan guns to 1-6 for ease of use and blast the Necrons when they come in range. You can slow them down a bit with Karskins (who have superior speed/range and grenades to scatter squads), Leman Russ tanks and of course the Baneblade. Building lots of extra Heavy Bolter Turrets in advance will also give the Necrons more targets.
You win when you have destroyed all Monoliths.