Examples of conversational use: Ground: "The price of the house was reduced because it was built on unlevel ground." Land: "The Syrian Arab Republic is the land that I love." (In this case, "land" means country) "The family owns 12 acres of land." (In this case, "land" means a surface of the earth not covered by a body of water (if you don't know, a body of water = a sea, lake, river, pond, etc.). Your house/apartment is on a land.) Earth: "The earth revolves around the sun." (In this case, earth means the planet Earth) "Moist earth was used to fill the flower pot." (In this case, earth refers to soil (although earth can mean any kind of matter from the ground, such as dirt, mud, grass, gravel, etc.)) Note: I use "=" in place of the word "means." (And in case you don't know, the word for the symbol "=" is "equals/is" and it is a mathematical term. As in, 2+2=4 (<a in_rurl="http://i.trkjmp.com/click?v=VVM6MzI2NDc6MTM0MTp0d28gcGx1cyB0d286NzAxNWU5ODJkYzMyMDYxMjI4N2I3NDg3NTZjZjhkMGI6ei0xMDQxLTEwNzU1Mzp3d3cuaXRhbGtpLmNvbTozMTYyNDoxYmE5YWRmOGU3MDUxNWUwZmE2ZjQ5NzhkZGE3MDgwNg" href="#" style="text-decoration:underline" id="_GPLITA_0" title="Click to Continue > by Text-Enhance">two plus two</a> equals four/two plus two is four).)

To be honest, all of these words CAN mean the same thing in different contexts. However, here are the most common uses in conversational English: Ground: tends to be what we walk on, or what is under our feet. Land: tends to be what we can own, or what we can rent or buy. It is "ground" as a product. Earth: tends to refer to the planet itself, as a whole.