The home city is the capital of your country back in Europe. You can change it's apperance and add all different stuff in it.
It also supplies you with free shipments. Once you get 1 shipemnt from doing various things (gathering resources, buildings,training soliders etc.) You get a shipment card. This can be resources, soliders, upgrades, mercs etc. The more you age up the better the cards are.
Once you have nice looking cards you put them in a 'deck'. This is a table with a selection of cards to choose from during a game.
The more you LvL up from gaining XP (from doing gathering resources, buildings,training soliders etc.) you can choose new cards for every LvL you up.
The higher the LvL the better the cards become.
I hope I helped.
My Heroes:
Kirk Hammet
Andrew Stockdale
Dave Grohl
Jimmy Page