Nitrous oxide has the chemical formula N2O and is composed of two atoms of nitrogen and one atom of oxygen. It is a greenhouse gas but is only very sparingly present in the Earth's atmosphere. It is naturally produced by soil microbes when they break down organic matter into base nutrients in a process called dentrification. It is not present in higher amounts in the atmosphere because it reacts with ozone (O3) that is also present in the atmosphere.
Nitrous oxide would be a dangerous greenhouse gas if present in higher levels for two reasons. One, it is an analgesic gas, meaning that it has medical properties. Commonly referred to as laughing gas, it is used as a anaesthetic agent in minor dental and medical procedures. The other reason is that N2O retains heat at a much greater level than other greenhouse gasses. In fact, it has about 300 times the greenhouse effect of carbon dioxide, so global warming would be an even bigger problem if N2O were present in higher levels.