Property Market is a place where you can buy companies (only organizations, parties and armies). Companies can be bought only for Gold and can't be moved later, check where is company located before you buy. To access it go to Market -> Property Market.
There you can choose type of company you want to buy. You can buy only on property market of country where are you located. Products and employees will stay in company when it is on sale. To find out how to put your company on sale check Company.