A Lewis structure is a representation of atoms and electrons that show how a molecule is constructed. Atoms reach their most stable state when they are surrounded by eight valence electrons (the "octet rule"). These electrons might be lone pairs--two electrons that are just associated with that atom--or covalent bonds--two electrons that are shared between two atoms. When there is a covalent bond, both atoms count the shared electrons as part of their 'valence spheres'. In a Lewis structure, lone pairs are represented by pairs of dots, while covalent bonds are represented by straight lines connecting two atoms. It looks like Lego27bricks is taking introductory chemistry, since his LEGO self is trying to figure out a Lewis structure.