COH 1 was on the western front, so the faction are US/wehrmacht. Singleplayer campaign are US only.

Expansion1: Opposing force adds 2 faction UK/Panzer. Singleplayer campaign for both british and Panzer corps. Adds AI challenge game mode.

Expansion2:Tales of valor has no new faction but add several more varity of infantry and vehicles for commander customization. 3 short singleplayer campaigns and 2 multiplayer game mode

COH2 is on the eastern front, germans vs soviet. Campaign only spans for the soviets, and challenge mode "theater of war" have both soviet and german short "campaign"

In short, COH2 is a refine version of COH1 with some eastern front flavor into the mix. Its much focus on multiplayer aspects than singleplayer

If you are new to the series, pick up COH1 and the following expansion since they are relatively cheap on steam. Once you are done with it, pick up COH2. COH2 is a much better built for multiplayer.

for example, i'm at the church and i got this tip that a random guy was missing. how do i take that mission? or do i just have to look around hoping i might find him? do i have to talk to someone for a lead?

also...

in the first part at the cabin there was a hurt girl. and it seemed like i needed to find medicine for her which i had a couple of painkillers and stuff, but i couldnt hand them to her, and after a while she died or something... was it my fault? how was i supposed to give her the medicine?

irotinmyskin

Post patch:

as for missing person, wait for a hint from lily to confirm the location of the missing surivor. Open your map and locate the icon with "missing survive". Head over there as quickly and rescue him/her - i believe the mission last for 1 day (IRL 1 hr) or else that person will be dead.

First part of the cabin is called ranger station, that area is a tutorial section where those people are supose to die. You could comeback to that location to visit it again

And outposts, I have no idea how they are supposed to be a supply cache works! 

ROCKNROLLCOWB0Y

How do you take out the Jugger with a vehicle? I'm trying to get the achievement for killing the freak zombies with a car. He's the only one left. I completely destroyed 4 vehicles continually ramming one and it wouldn't die.

nm15

i m not particular sure that different cars having different damage. As far i know it only require 2 rams "in a sucession" from most vehicles. First ram will stun it, and 2nd ram will finished it.

GUIDE:

http://youtu.be/PDDG9eEZLAg

Overwatch only fires once enemy is on the move (exception of Support - Reaction fire skill). All overwatch has a penalty of -10? aim on top of your regular aim percentage (except for Sniper - overwatch skill). Generally overwatch is used for covering blindspot (out of line of sight) at mid/close range which is extremely useful in CQC especially inside of Large alien spacecraft. Out in the openfield Overwatch is useless (except a LT. Sniper)

Alternatively, overwatch could be use "bait & kill" to great advantage. 1 example of effective use of overwatch will be against "berserker", by positioning your overwatch units at a blindspot facing the intended path of the enemy, bait 1 of your units by firing at it.