Mirror mode

how do i edit on boths sides, when i model a cube with mirror mode on?

i can only edit on one side

yeah im a noob.

Mirror modifier is to substitute laziness… If you do not feel yourselves as a lazy person you could press triangle looking icon on Mirror modifier’s tab - that will make points editable on both modified mesh sides ;).
It is a bit hard to tell what exactly is going on your image - if that is a mirror line where mesh had been pushed over the symmetry, enable Clipping option on Mirror modifier and move points so that they merge on the symmetry line.

thanks ! it helped!