There are three main types of car jacks.
1. Floor Jacks, also known as garage jacks or trolley jacks, is a hydraulic jack that offers an outstanding balance of strength and stability. Since they are on wheels, they are easy to slide into place. Once you've made sure that the floor is flat and even, you position the jack under the proper jacking points, lift the jack's arm up and down, and pump until the desired height is reached. Keep in mind that floor jacks are heavy and on the bulky side.
2. Scissor Jacks are much more common because they often come with purchasing a car. They are lighter and smaller, making them easy to store in your car. They are usually ideal for performing a tire change, but for more hands-on repairs requiring you to get under your vehicle, then you should look into something more stable and reliable like a Hi-lift jack, a transmission jack or a floor jack. And don't forget, once your car is lifted, you should always use Jack Stands for added stability and safety,
3. Bottle Jacks are very similar to floor jacks but tend to be smaller and less bulky, allowing you to transport them more easily.
Is it safe to get under a car on jack stands?
If the surface your vehicle is on is flat and level, and once your vehicle is lifted using the appropriate jack for the size and type of your vehicle, then yes, it is generally safe to go under it while always using caution.