Child car seats that can be installed with ISOfix usually have to solid arms that connect to the metal ISOfix points in the car. There is usually also a third point of support, either a support leg that touches the floor, or a tether, which is like a piece of seat belt that hooks onto an anchor point on the back of the seat or in the boot of the car. The tether and the support leg have the same effect in the event of an accident, they will both stop the forward momentum.
The picture below shows the tether points in a Dodge Journey, but they can also be situated on the floor of the car, further up the seat, or on the top of the seat (so confusing right?) They sometimes have a picture of an anchor next to them, but not always. If you're unsure if something is a tether point check your car's manual, or feel free to pop into our store and we can check for you. Mistaking the something else for a tether point is one of the most common mistakes when installing a child car seat incorrectly.