The nasal septum is a thin sheet of cartilage and bone inside the nose separating the right and left side. It can be bent from an injury to the nose or sometimes is just formed with a deviation. If it is persistently causing nasal blockage it can be straightened with an operation under a general anaesthetic.
This leaves you looking the same on the outside but the inside is straighter allowing for a smoother flow of air through it. The procedure is called a septoplasty.
Apart from the septum other causes of nasal obstruction include nasal polyps, rhinitis and hypertrophied turbinates. Turbinates are sausage shaped fleshy rolls inside our nose to warm and humidify the air. Sometimes these become overgrown. They can be shrunk with a variety of techniques.