OK, let's take this step by step ....

You have an equation. (because there is an equal sign.)
It needs to be solved, which means find values for the variables #x and y# which will make it true.

There is a problem! If it had ONE variable, like just #x#, it would be easy... If #3x +4 =25#, we can work out that #x =7#
BUT, there are TWO variables .....this means there are many, many values for #x# and #y# which will make this true.
#3" "# Find some values which work .... this means choose an #color(red)(x)#value and work out a #color(blue)(y)# from the equation.
It will help to choose EVEN values of #x#, because we need to divide #x# by 2 and then multiply by #3# and add #12#."
If #color(red)(x=6)# .... what is #color(blue)(y)#?
#y = 3/2 (color(red)(6))+12" "rarr" " y = color(blue)(+3)#
If #color(red)(x=10)# .... what is #color(blue)(y)#?
#y = 3/2 (color(red)(10))+12" "rarr" " y = color(blue)(3)#
If #color(red)(x=0)# .... what is #color(blue)(y)#?
#y = 3/2 (color(red)(0))+12" "rarr" " y = color(blue)(12)#
If #color(red)(x=8)# .... what is #color(blue)(y)#?
#y = 3/2 (color(red)(8))+12" "rarr" " y = color(blue)(24)#
#4" "# So you can see that for ANY value you choose for #color(red)(x)# , you can find a matching #color(blue)(y)# answer.
So far we have the following pairs of values: #(color(red)(x,color(blue)(y)))#
#(color(red)(6),color(blue)(3))#, #(color(red)(10),color(blue)(3))#, #(color(red)(0),color(blue)(12))#,#(color(red)(8),color(blue)(24))#
You could do this over and over and over..
This step is often done in the form of a table.
#5" "# Plot points means: now that you have worked out matching pairs of #(x,y)# values, draw up a set of axes and plot the points on the grid.
The #x# is the first number and the #y# is the second.
If you plot (draw/mark) the points we have shown above, they will all lie in a straight line and you can draw a line (graph) through them. graph{y = 3/2x+12 [15.42, 24.58, 5.36, 14.64]}