You click on the arrow tool at the bottom right of the screen then you get a slide up menu then click the plow tool.
To fallow/plow land, it costs 15 coins per square. You can also just leave the land un-plowed and it will not cost you anything. However, you won't be able to grow anything if you don't plow it.
search farmville in the searchbar and follow the link that's all
First you have to join Facebook and become a member once you have your own page you can then search for " Farmville application" and play it.