You start the game with three fields - two of them are located close to your farm. Each field is in a different state - on one of them, you will find ripened crops, the second one is waiting for sowing and the third one needs cultivating. Fortunately, you have all the necessary equipment, so get to work!
Switch to the tractor located near the field no. 38. Attach a cultivator and hire a worker. Next, switch to the machine on your farm, near the sowing machine. Attach it to a tractor and refill it (it costs about 360$). Go to field no. 24 and start sowing (wheat or barley). Here, you should also hire a worker, as the tank in the machine won't be emptied. On the last field, you have to harvest the crop. Use the harvester located nearby - as you don't have much to do at the moment, you can perform the task yourself, instead of hiring a worker.
Attach a header to the harvester and lower it. Remember to drive in a straight line and harvest as much crop as you can every time. When you set the machine in the right place, you can switch on the cruise control. When on the other side of the field, turn around and repeat the task. After the container is full, drive to the trailer nearby and unload the grain. If you've decide to hire a worker, you can help him by driving a tractor next the harvester, which will allow you to collect the crops onto the trailer and the worker won't have to stop.
When doing things in the order described above, you will have all the necessary task completed on all three fields. Now you only have to wait for the planets to grow.