The picture below gives you a basic understanding of forces and how they are omnipresent -- even when nothing seems to be moving. Here, instead of moving an object, forces are keeping the apple on the table. There are forces associated with both the apple and table. Your job is to determine the forces acting on the apple and the force on the table due to the apple.
Using the instructions in the pop-up window in the upper left corner of your screen, attach the correct "force arrows" to either the apple or the table. Make sure to indicate what KI D of force your arrow represents.
When you have finished and are certain of your results, click the "check" button to verify your results. Don't be discouraged if you don't get it on your first try. Give it another go! After a couple of trys, the correct answer will be displayed.