What is the use of towns in the game? I just played one quick game but then I dove more into the rules and I am looking forward to play the game again on friday so I want to be sure in this:

The Strongholds and Cities provide Victory Points, towns dont.

When attacking the City of fortification the attacker has a little disadvantage in the first round. When he is attacking the Stronghold he is limited during the whole battle. But there is nothing about he towns in rules again.

Only thing I found is that the towns are good because can muster (recruit) there, is that so?

Towns can be used for mustering. Capturing them also affects a Nation's political status, as the Nation will be moved on the Political Track. They can also provide some shelter for the Fellowship, as some Shadow Event cards that target it can only be played if the Fellowship's Last Known Position is not in a Free Peoples Settlement.

One more Question. I just need to clarify this. When my army is attacked in region that has a Fortress I can retreat right into the Fortress even without the first combat round (no casulties) right? So in order to attack me in the fortress my opponent has to spend one more Action die...?

While retreating in region that does not have a fortress (only city, town etc.) I have to fight the first round (if I dont use Scouts or something) and then I can retreat in free or ally adjacent region, right?

Yes, that's correct.

Fortress or stronghold? Fortress acts lile a city- first round of combat attacker needs 6's. It's the stronghold you can retreat to, which ends the battle action until the attacker seiges it.

There is actually no such thing as a "fortress" in the game. The correct terms are Stronghold and Fortification. From the context, Rozy was talking about Strongholds.