At the bottom of easyuo are a bunch of numbers, as you move the cursor around one set of those numbers will change. these are your cursor positions, and that is what you are trying to change.
set %x #CONTPOSX + 306
means you want the cursor to move to the gumps x position plus another 306
x being the up and down movement
y being the left and right movement
the easiest way for a beginer is to move the gump to the top left corner of the game window, until the
#CONTPOSX #CONTPOSXYand in the right hand pane have values of 0. Then move your cursor to the area on the gump that needs to be clicked. the numbers at the bottom in the cursor box will be what you need to change the numbers. You still need to write the line as
set %x #CONTPOSX + 306
since you will not always have the gump at the 0.0 position
another way to move the gump to the 0.0 position is to open the gump, make sure it is on top, and run the following code
set #CONTPOSX 0
set #CONTPOSY 0
halt