This scenario enables many level 1 upgrades for some of the more popular common cards. So you are probably going to be playing it again... and again... and again, trying to get those upgrades. The upside of this is that it features a good example of a wall defense. So it offers the possibility of trying out many defensive deck strategies.
Since it is the first scenario that a player new to Battleforge encounters, a bit of extra detail is in order for the walkthrough. Any basic starter decks should be largely sufficient to beat the standard scenario.
Build some melee units and archers (recommended 3 of each), and help Rogan and his forces clear the area up to the first gate. This should give you access to build an extra power well and your 2nd orb. Build 3-4 of your 2-orb creatures (Firestalkers come in handy) and make sure all your units are fully healed before proceeding through the gate (if you don't have healing spells, move your forces close to one of your power wells or monuments to heal).
Proceed cautiously through the gate, and wait for the enemy to attack after about 20 seconds. If you are close enough to the gate, Rogan's forces will come and help drive them off. Once that is accomplished, move east towards the nearby power well and destroy the enemy building there using ranged units so as not to provoke the nearby enemy garrison units from sallying forth. Build the power well and then move your forces south to the other power well there, and build it quickly. This should provoke a new enemy attack, but this time you will be fighting near one of your own power wells, so your units will heal as they fight.
From here, move southwest and finish off the enemy building and tower you find there, and secure a 3rd orb. Heal your units and build a few 3-orb creatures.
Now move east and destroy all the rest of the enemy creatures and buildings you find in the area. Make sure you have built all available orbs and power wells. Once you clear all enemy units, Rogan's forces will advance and he will unlock the next gate.
You can either build a defensive line around the wall section you are given and use the Screaming Stone to summon a horde of enemy units, or build an offensive army and progress forward and clear the enemy camps. For beginner decks, the defensive wall is probably easiest. If you choose the defensive route, fill the battlements with your archers and build 2-4 towers. Make sure to add 4-6 of your 3-orb creatures to your small army and position them ready behind the wall before activating the screaming stone. It is also nice to have enough resources built up to use some Direct Damage Spells on the clumps of enemy units that swarm against your gate if you can.
If you build a defensive wall, you can optionally lure a few groups of enemy units toward you, but this is not absolutely necessary. If you opt to clear a few out, the Screaming Stone can bring the rest. This is helpful if you find you get overwhelmed when you summon all the enemy units at once.
Proceed through the gate and build the remaining 3 power wells and 4th orb that you find in the newly unlocked area. You are now tasked with fighting a large Boss type monster who will wait patiently for you to build up a huge army, cap out your unit limit, and mine all available resources from the map to be able to cast spell after spell in his face (it is actually not necessary to do this, but it is true).
Adding a few more 3- and 4-orb creatures to the survivors of the wall attack should largely suffice (provided your forces weren't decimated at the wall). In all, you want maybe six 3-orb creatures and four 4-orb creatures as the main body of your attack, supported by whatever else you happen to have. Melee units will hinder the boss mobs abilities to cast spells, so don't just go in with an army exclusively composed of ranged units.
The mechanic to watch out for in this fight involves spirit mobs that spawn in and slowly float toward the boss. If they reach him, they grant him some interesting abilities. He can self heal, freeze your units, cast offensive damage spells, and has some knockback spells. My preferred strategy is to get ranged units that have explosive damage that causes knockbacks. With enough of these bombing the main boss, the spirits will never reach him. You can also build towers around him to help with damage, although it is probably best to stick with replacing your melee units as they die, so as to prevent the Wrathgazer from targeting your main ranged heavy-hitters.