Below are just a general info about outposts. For defense and raiding go here:

There are two “Resources” involved with Outposts:
Trade Goods (TGs) – You can win these from Raids and Cycle rewards, and spend them in the Trade Good Store.
The amount of Trade Goods available in a raid are determined by your Player Level, and the “Walker Strength” of the person you are raiding.
Influence – Influence isn’t a spendable Resource.
Influence is won and lost during Raids.
You win Influence by killing the Defenders when you Raid someone.
You win Influence when your Defenders kill all the attackers when someone raids you.
You lose Influence when your Defenders are killed when someone Raids you.
You lose Influence when you get all your Attackers killed when you Raid someone.
Influence determines your Ranking on the Leaderboard.
Influence determines your Cycle Reward.
The two buildings related to Outposts are:
Outpost: This building generates Trade Goods and also determines what maps you are able to use as your Outpost Defense.
Walker Pit: This is where you spend Trade Goods to capture and upgrade Walkers to help defend your Outpost.
When a Raid occurs, there are 3 objectives:
Capture the Flag
Capturing the Flag must be done first, and allows you to proceed to the next 2 objectives.
If you don’t Capture the Flag when attacking, you will lose Influence Points.
Grab the Trade Goods Crate
For most players, this is the most important objective, and all that really matters.
If you are Attacking, Grabbing the Trade Goods Crate gives you Trade Goods as a reward. After Grabbing the Trade Goods Crate, you can “Complete” the Raid and KEEP THE TRADE GOODS & NOT LOSE ANY INFLUENCE.
If you are Defending, and an attacker grabs your Trade Goods, YOU LOSE NOTHING! You don’t lose any of your Trade Goods, and you don’t lose any Influence. This is very important to know.
Kill the Human Defenders
Killing the Defenders is the only way to get Influence from a Raid.
Having your Defenders killed is the only way to lose Influence when you Raid someone.
To participate in Outposts, you need to build your Outpost Building and Walker Pit, and then proceed to “set up” the Outpost. If you don’t “set up” the Outpost, you can’t be raided by other opponents, and you can’t raid other opponents.

Matchmaking for Outpost Raids is determined by your Influence and Player Rating.
When defending against opponents, your Walkers will never attack your Defenders!

Info taken from: