1st Law
Learn this- "The velocity of an object will remain constant unless acted on by an external force"
When you add all the forces on a stationary object the result is 0 When you add all the forces on an object moving at a constant velocity the result is 0
2nd Law
Learn this- "The rate of change of momentum of an object is equal to the resultant force on the object"
When you add all the forces on an accererating object the result is not zero. In other words there must be a force Many students think Newton's 2nd Law is F=ma , this is technically wrong. F=ma is a result of Newton's 2nd Law. Don't fall for this trap.
3rd Law
Learn this- "If an object A exerts a force on object B then object B exerts an equal and opposite force on object A"
There are 2 forces mentioned in Newton's 3rd Law but students make mistakes because they dont realise that 1) The two forces are on different bodies 2) The two forces are equal, but in opposite directions 3) The two forces are the same type (they are both gravititional or both electomagnetic or both nuclear)