The atomic number of carbon is #6#, which is also the number of positively charged protons its atomic nuclei. If the atom is neutral, it will have the same number of negatively charged electrons. Its electron configuration is #"1s"^2"2s"^2"2p"^2"#. The orbital diagram shows how the electrons are arranged within each sublevel. The maximum number of electrons allowed in an orbital is #2#, each with opposite spins (Pauli's exclusion principle).
In a neutral carbon atom, the #"1s"# sublevel has one orbital with two electrons with opposite spins, represented by the arrows pointing in opposite directions. The #"2s"# sublevel also has one orbital with two electrons, also with opposite spins. The #"2p"# sublevel has three orbitals. According to Hund's rule, each orbital must contain one electron each with the same spin, before adding a second electron. So in the #"2p"# orbitals there are two electrons, each with the same spin, and the third orbital is empty.
