Anytime we need to get the equation of a line, we need two things
a point 

a slope 
ALWAYS!
So, what do we do if we are just given two points and no slope?
No problem  we'll just use the two points to pop the slope using this guy:
Check it out:
Let's find the equation of the line that passes through the points
This one's a twostepper...
STEP 1: Find the slope