I can only breathe through one nostril, what can i do to open up the other?

Why only 1 side?: Is it always the same side that's open? Have you suffered trauma to the nose/face? Do you have other symptoms? You didn't really give us enough to go on. See an ENT who can help tell a nasal tumor from septal deviation or chronic nasal irritation from other sources.

Deviated septum?: a deviated septum can be corrected surgically to bring the septum to the midline. If there are symptoms like nasal obstruction, snoring or recurrent sinusitis, have your nose evaluated by a board certified otolaryngologist.