Progression

Hello, I am pretty new to the study of science and I was just reading an article on wikipedia about Newtons laws . I have a few questions on this and hoped somebody would kindly answer . 

Quote

Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. More precisely, the first law defines the force qualitatively, the second law offers a quantitative measure of the force, and the third asserts that a single isolated force doesn't exist. These three laws have been expressed in several ways, over nearly three centuries,^[a] and can be summarised as follows:

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First law:	In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.[2][3]
Second law:	In an inertial frame of reference, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma. (It is assumed here that the mass m is constant – see below.)
Third law:	When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

 

 

From: https://en.wikipedia.org/wiki/Newton's_laws_of_motion

What does it mean by a quantitative measure of force ? 

What is an inertial reference ? 

Is there a Law on acceleration ?