These gears have a different use, and you cannot use first gear in the situation where third gear is required.
Inappropriate gearing can bring havoc to your vehicle and cause your vehicle to get stalled. You should have an idea about the proper functioning of these gears.
The first gear of your vehicle is for driving through the downhill and those areas where slow speed of your vehicle is required.
You can shift the gear to the third one when there is a need to increase the speed of your vehicle.