Isofix provides a more secure and easier way of fitting car seats in cars. Most cars now have anchors built into them to attach an isofix base to. To find out if your car has Isofix points, look for Isofix labels between the base and back of your car seats (the fitting points themselves may also be visible) or check your vehicle's handbook or contact the manufacturer or dealer.
The isofix attachments on the base will attach to the anchors in your car, an additional top tether or support leg is used to prevent the child seat titling or rotating in an impact. This removes the need to use a seat belt to secure your childs seat. You car seat then clicks onto the isofix base.
There is no universal isofix base, each car seat will have specific base to go with it.
Maxi Cosi isofix bases: Maxi Cosi have three isofix bases, easyfix base, familyfix base and the 3wayfix base(which has now replaced the 2wayfix base) depending on which maxi cosi car seat you have will depend on which base you will need.