At the top left of the screen in your city, you can see your rank right under your avatar. If you click on that, it leads you to the rank list. You can search for a player's name and then click on it and choose "visit" to see the player's city. You can visit the city of any player in your world using the rank list, even if you have not discovered the person.
Overall, I would suggest building workshops and residences to start accumulating gold and resource points -- those are the basic things you will use in your city. My personal choice has been to develop my economy as well as my military -- if you want to do that, you can build a barracks and start producing military units.
You need culture buildings in order to keep upgrading your city. One tip on culture buildings is that they don't need to be connected with roads, so you can stick them all someplace away from your main hall and save the spaces around roads for the buildings that require them. Having more than the minimum culture buildings will allow you to collect bonus gold and resource points. Whether this is beneficial to you or not depends on your strategy -- some people choose to have fewer culture buildings and more workshops and residences to have a higher base production.
The way to progress in the game overall is to accumulate knowledge points. You get one every hour, and you can buy more with gold or solve encounters on the map to gain one resource point per encounter. To solve encounters you can either pay with resources or fight battles. I choose to do a combination, like I will pay with resources when I can use my "boosted" resource, which it sounds like in your case is marble.
Like others have said, I wouldn't worry too much about being "stuck" on a quest that you can't decline. You will probably finish it eventually just in the course of playing. The quests that give you the option to Decline are repeatable, and if you're stuck on one of those quests, it's best to just decline it and go on to the other ones until you can complete it. (I run into that most often with the quest that wants you to build 2 buildings above level 3.)
It is good to explore your neighborhood and get to know your neighbors -- they can provide neighborly help and also trade resources with you that you will need later. The more encounters you solve and hexagons you scout, the more neighbors you will have to help and trade.
Basically just keep building and gaining supplies and troops, scout the map and solve encounters as you are able, and over time you will progress.