In the Placeable menu, you will find all the elements that you can place somewhere on the map after buying. To do that, choose the building that you're interested in and a map will appear, on which you can put it anywhere (Except for fields). After selecting a place, an appropriate amount will be taken from your account and the object will start working. When wandering through the map, you will find it exactly where you've put it.
The main function of buildings is to generate profits. Three of the available objects do not require any attention - beehouse, solar collector and wind energy converter generate a given amount of money every hour, without any further requirements. Greenhouses however, need two things - water and manure, to start bringing profits.
Water is easy to provide. You just have to buy a mobile water tank (7000$) and replenish water (you can do it in the wells located on your farm or near the cowshed).
The thing is a bit more complicated (and more expensive) with manure. First of all, you need to have several cows that will produce it. You also need a loading wagon, on which you can load straw. You then need to deliver it to the cowshed - only then will the cattle start to produce manure. The last thing you need is a loader, on which you will load the fertilizer.
When you have all that, you can transport it to the greenhouses you have. An empty tank will take 2000l of water and 3000l of manure, which will suffice for a few days. Your task is to remember about providing it again.