Your basic troop is the Recruit and you will need them in the thousands, mainly as cannon fodder. Set up your production chains right from the start to keep a supply of these guys coming and they will help you clear the early areas fairly easily. Once you gain access to bowmen you will note they are longer and harder to produce and so its worthwhile losing 2-3 Recuits instead of replacing a Bowman, this is a methodology that holds true throughout the game.
Always have your recuits take the damage to protect every other kind of military unit.
Knowing how to tackle enemies is also important and seeing that maybe adding 50 Recuits to a battle might only give you a -1 to possible losses can inform how you and when you attack.
Forming an Army.First you need a General, they can be bought in the Tavern for increasing amounts of gold (special ones are available for Gems in the Store and during Events), buy one and then click on him in the Star Menu. Place his Garrison on the map.
Click the Garrison and add troops using the sliders. You now have a force to attack. Click Attack button and click on a camp to attack it. Note you can retreat your army in this menu too which handy when caught by an unintended camp or as a tactic.
Area of Effect.Click on an enemy camp and a red box will appear and show you the area of effect that camp has, stray into that area more than 1 pace and you will be drawn in and attack that base (Note that Leaders Camps have no area of effect).
You can Retreat if you are quick and avoid fights you never intended.
For more details see the Area of Effect section.
Fighting Rounds.Your attacks go in waves with "First Attack" units going first, then your infantry troops, then ranged troops and lastly your general. This usually puts your Recuits up front to take all the damage, later Cavalry will come into play and they take a first swipe but with their low hit points you want to be sure the Enemy is wiped out before they can retaliate.
You can view this process by opening the email you get after a battle and pressing Replay to see how the attacks actually happened. It's worth storing these emails for a short time incase you suddenly notice a loss of troops and want to know why.
It is worth noting that if you get a mysterious loss of troops, i.e. not lost in battle, left on an adventure island, in transit, you should review your emails and if you find no apparent reason for loss you can submit a problem with the game to the Dev team via the Contact Support button on the website. They will review the situation and send you suitable replacement weapons via email, you will need to rebuild them at the Barracks and so all you lose is time.
Failed Attacks.If for any reason all your troops are wiped out and your General becomes injured (either by design at later levels or by mistakes earlier on) he will return home dejected. The bright trumpet sound of success replaced with the melancholy drums of defeat. Never fear he isn't dead but he will take 4 hours to recover after which he can be used as normal.
As a side note you can tell when an attack you make is succeeding as a red-green meter appears and slowly counts down to a successful conclusion for your troops.
Planning battles in Advance
There are several websites that help you plan your battles to mimize losses and by far the best one is the Kampfs Simulator. Visit: http://settlersonlinesimulator.com/dso_kampfsimulator/en/ to plan your battles using the scrolling boxes and the drop downs to automatically populate the values of battles on various Adventures and your own island.
Early in the game you can manage with a single general but once you are able to house over 200 troops you will need a second one. Once you reach Level 26 and Aventures 3 Generals is pretty much a must to ferry enough troops into the warzone (basic is 30mins each way travel to an Adventure).
For the most part you dont want your general to be left alone and if your army is wiped out he will almost certainly get injured causing him to retreat to his camp where he recovers over the next 4 hours. After 4 hours he can organise his troops and attack once more.
Blocking uses a trick to stop an area of effect that covers a target camp from distracting your army. This tactic can be used on many Adventures and is worth getting to know. Please see our Blocking Article to find out more.