hi. hello ... weird title , isn't it ? anyway :D,I am new with the AutoCAD and i have a silly little problem .. WTH is this, and how i remover it, it come every time i apply a command

These icons are autoconstraints. You can switch it off and on with the AutoConstratint icon in the bottom status bar (Ctrl+Shift+I) or via the Parametric ribbon.

And in this case it means that the two lines will always be perpendicular to each other and each end coincident at the point where the small blue square is.  Unless you remove these constraints they will always keep this condition regardless of how you might move one of them.  To see this for yourself, grab and move one of the lines and watch what happens.Dave.

Thanks alot