The nucleus of an atom has only positive charges. The other part of the atom is the cloud of electrons which surround the nucleus. Electrons have negative charge. A neutral atom will have exactly as many electrons as it does protons. This makes the net charge of the atom zero.
Atoms can be ionized. This means that they have fewer or more electrons than protons. Having fewer electrons an atom is said to be positively ionized. Adding extra electrons makes an atom negatively ionized. Negative ions are typically unstable and will expel the extra electron. But they can be stable for some period of time.