Before you make a business you need a Building Permit, you can get these from the master builder when you have a 100% trading record, to make this increase quickly, give the max to Church and give the max for soldiers or cannons and if you want, do a bit of trading.
Building
To build anything, you need a free space as well as enough wood and stone. If you don't have enough in your warehouse, you can try to buy from the town for the regular price. If the town also hasn't enough materials you can't build anything. When you try to build a warehouse, which is necessary as the first building in an town, you can have the materials on a convoy in the harbor. Each building, with the exception of homes has a building time. Only after this time is up, will the building fully function. To have a business produce anything after it is finished, it also needs workers. Every Business needs 30 workers. To get them they will hire the available settlers in the town. You may need to ship workers from another town to get the businesses working. If you do need to ship workers, go to Govenor's towns first, they get transport convoys with workers going to them and they usually have a higher wealth level so you are more likely to find workers there. If there are enough settlers available, they need houses. Every worker will found a family so hell take 4 places in a house. One house can fit 120 people so remember to make sure, to get enough houses. Living space is also needed for soldiers, who only need 1 place per person, so don't wonder, when the number of used places doesn't mach the number of workers * 4. At the start try to avoid products that need a colonial good because you are stuck if the transport convoys fail.
Costs
You should now click on your storehouse and get that to automatically sell the product (or if you have one, set up a trade route but take from the warehouse). If you are buying, set up a trade route or set the warehouse to buy (expensive usually).