Slope; A measure of Direction In my book, the definition of the slope of the straight line is:

The slope is a measure of the direction of the line.

1) When the line has no slope, it tells that it is vertical or moving vertically along the $y$ and $y'$ axis.
2) When the slope value is equal to $0$ it tells that the line is moving horizontally along $x$ and $x'$ axis. 
3) When the slope value is positive, it tells that the line is rising to the right. 
4) When the slope value is negative, it tells that the line goes downward to the right. 
5) A large positive slope value tells that the line goes along the $y-axis$ and is rising steeply to the right, and a small positive slope value tells that the line goes along the $x-axis$ and is rising slowly to the right.
Well, I'm not sure about the fifth one. Do a large positive slope value and a small positive slope value judge the direction of the straight line or if its rising steeply or slowly, does that judge the direction of the line?  
 A: 
Do a large positive slope value and a small positive slope value judge the direction of the straight line or if its rising steeply or slowly, does that judge the direction of the line?

Both:
You can use slope to determine how steep a line is; if a line is steep, it's slope will be larger than a line that is less steep, and the steeper the line, the larger its slope.
So they are mutually correlated: steepness increases as slope increases (directly and positively proportional):  (each gives information about the other...
But steep, as a description itself, is relative to some orientation. Usually we mean that steepness is a measure of the absolute value of the slope: the larger the magnitude of the slope, the closer a line with that slope is to the y-axis.  
The sign of the slope tells us in what in what direction the line is tilted, if it is "tilted" whether y is increasing from "left to right" (positive), whether $y$ is decreasing from left to right, or neither(0 = horizontal, or slope is not defined = vertical.)
A: Take a few of these examples.
a) $y= x+1$ 
b) $y= 10x+1$
c) $y= -10x+1$
In line a, we find that the slope is x which is equal to $\dfrac 11$ which means rise 1, run 1. The graph is positive due to the slope being positive. This also means it is going to the right.
In line b, we find that the slope is $10x$ which is equal to $\dfrac {10}1$ which means rise 10, run 1. The graph is positive due to the slope being positive. This also means it is going to the right.
In line c, we find the slope is -10x which is equal to $\dfrac {-10}1$ which means drop -10, run 1. The graph is negative and goes to the left.
All of these graphs have the same y intercept, the only differences is the slope. 
Examples B & C are very similar, the only difference is that C has a negative slope and goes to the left and B has a positive slope that goes to the right.
Another thing to point out is notice the steepness of example a vs. b and c.
This might be a handy tool to help you visualize these examples: https://www.desmos.com/calculator
