I'm setting up dialogue area and I want to use a complete transparent area, i don't know if it's possible because when i click the edit button it shows the dragable big cursor and not the little one for edit polygons. Also to set the position in the scene where the dialogue with lines has to appear?
Just create a transparent png/webp image file at the size & width you want the dialog interface to be & add that as the interface background. As for the positioning, you might need to drag the bottom window form up with the options on to be able to see the x & y position input boxes - sometimes they are hidden (depending on size of your monitor & the default size of the form).
Quick note: first red outlined bit in the image attachment controls the height in pixels between each dialog line & the next outlined bit determines the position of the dialog interface on the screen - note that position is based on top left corner, so... if you have a dialog interface the same width as your default game resolution then x should be 0 & let's say the interface is 200px high & your default game resolution is 1920x1080, so what you would do is subtract 200px from your game default resolution height. 1080 - 200 = 880. So y = 880.