Newton's 3rd law states that for every action there is an opposite and equal reaction. Put another way when you push on an object it pushes you back.
Newton's 3rd law starts with conservation of momentum Conservation of momentum states that the total change in a system’s motion to be zero. As a result moving a mass requires moving another mass in the opposite direction.
Rockets are the best example and the flame that is seen coming from the bottom of the rocket is propellant mass that is being ejected from the engines. This mass provides the action whose reaction pushes the rocket forward. Jets work on same basic principle but the main differ deference between a jet and a rocket is that jets take in air as part of their propellant mass making them more efficient than rockets since they are nor required to carry all that mass onboard.
The basic concept of Newton's 3rd law is that two masses push on each other with equal force. Equal mass will move away at the same speed. When one mass is smaller the other and if the force is kept the same, the smaller mass moves away faster and the heavier mass moves at the same speed as before. If one keeps the masses the same as in the last example but this time the force is larger then they both fly apart faster. The smaller mass still moves much faster than the larger mass.
One thing that is a little counter interactive is the fact that when a car that is being driven down the road, the Earth is actually being pushed in the opposite direction. To be fair this affect is extremely small but it is sill not zero and the traffic that is going opposite direction averages out to zero net force. It gets even stranger since even when you are just walking around you are actually pushing the Earth in the opposite direction. Once again it is still an extremely small, in fact much smaller than in a car; but still not zero. Furthermore all the people and animals in the world the affect will still average out to be zero. Like wise when a planet moves around its star the planet pulls back on the star causing it to wobble slightly. This is a main way that extra Solar planets are detected.
Newton's 3rd law of Motion boils down to the fact that when one object pushes on another object, the second object pushes back. It is an important part of every change in motion in the universe because with out it no changes in motion would ever occur in the universe.