I think he's asking how to drag (a mouse click), in which case you would use
SCAR Code:
MoveMouse(x,y);
HoldMouse(x, y,True);
MoveMouse(a,b);
ReleaseMouse(a,b,True);
This would move the mouse to position x,y then left click drag it to a,b before letting it go (note: you probably shouldn't use this in runescape as it doesn't look like it has been updated in SRL and you would have no use for it anyway).
I just used movemouse as the other 2 procedures aren't SRL, but feel free to use MMouse instead of them.