The flight is the quickest and best means to arrive in Nepal, regardless of the country you belong to. A large number of flights land in the runway of Tribhuvan International Airport (the only International Airport of Nepal) in Kathmandu every day.
Some of the airlines that serve this airport are:
[Note: Gautam Buddha International Airport is under construction and will be in operation soon.]
You may also come to Nepal via the border of India, or through Tibet. It is a cheaper option than flight, but not recommended means of transportation as it takes long time to arrive in Nepal.
All baggage must be declared and cleared through customs on arrival and departure. Prohibited goods are not allowed to take in and out of the country.