Press the STAT button.
Select 1: Edit under the Edit tab.
Enter all x values into the L1 column. Simply press enter after each entry.
Now enter all corresponding y values into the L2 column. When finished double-check that there are equal numbers of x/y entries.
After entering all data into each list you must return to the STAT menu.
Go to the middle tab entitled CALC. Then select 4:LinReg. This is the linear regression function.
Once you see LinReg on the home screen, then press enter again.
You should now see the following format for your equation. The letter a is the coefficient of x (slope) and the letter b is the constant value at the end of the equation (y-intercept).
This process works for both modeling equations for lines of best fit using large sets of data as well as finding the equation of a line given two points.