Question: In my text book they said that:

> 
> 1. If no resultant force acts on an object, it will not accelerate; **it will remain at rest or it will** **continue to move at constant speed**
> 2. If an object is at rest or is moving at a constant speed in a straight line ,we can say that there is no resultant force on it.
> 
> 
> 

Now my question as it concentrates more on the first point.

How if the resultant forces or force are zero still the object moves at a constant speed and some times it does not move (or it is at rest as they say)?

Answer: 
A small and simple analogy to get the basic insight:

If each month, you spent as much as you earn, you will have constant savings.
If you started without savings, you will continue to have zero savings. 
If you started with \$1000, it will remain \$1000. In short: with net revenue zero, your savings are constant. Change revenue in force and savings in velocity, and you get what you need.
For an object to change from its state of rest to motion needs some force. When a force is applied the velocity of the object changes from 0 to some velocity V (and it keeps increasing as long as the force is present). This change in velocity is termed as acceleration.

Now if you remove the force, the object will move with the constant velocity V provided no other force is acting on it.