Missions allow the player to gain extra cash using farming machinery needed to complete them. They are timed and if you are not quick enough, you will fail the mission and get no reward. However, you will get an extra reward for completing the mission quickly.
Frequency of appearance for missions can be changed on the settings screen while in-game. When a mission is offered, a window will appear showing the mission goal and reward. Below, there are two options: accept or deny the mission. If you deny the mission, the next mission will appear when the next interval is scheduled (2 min, 5 min etc.), if you accept the mission, you will have 10 minutes of real life time to start the mission. The green circles on your PDA will lead you to where you need to go. If you do not start the mission in that 10 minutes another tab will pop up saying you have failed the mission. Do not worry, there in no penalty for failure. Always remember to do these missions ASAP, as you can easily become distracted and forget to do them.
In a mowing mission, you are required to mow a certain area. The timer will begin as soon as you mow any grass at the right spot. The amount of time and the reward depends on how much grass you need to mow. You do not have to mow all the grass at the mission spot, just most of it.
Tip: To save you good amounts of time and labor, it is recommended to purchase a set of three cheap tractors and cheap mowers to park them near every mowing spot (there are exactly three such spots on each of the official maps of Farming Simulator 2013). Any cheap tractor and the Kuhn FA367 from the free Farming Classics DLC pack are perfectly suitable for this purpose. This strategy will allow you to have a strong source of income throughout most of the game.
In a transport mission, you are required to move a pallet of goods from one area to another using a front loader and pallet fork. The timer will begin as soon as you move the pallet off the pad it was resting on. The time allowed depends on the distance you are required to travel. The reward depends on far you had to go. When you reach the required destination, there will be a spinning green circle on the ground where you need to drop off the goods. You don't need to place the pallet in the circle, just drive over it.
Tip: The transport mission usually require much more time and effort to complete compared to the grass mowing missions. It is generally recommended to ignore them unless you can afford to have a fast front loader parked near every mission start spot to minimize the amount of time needed to actually to start your delivery.