One can get to Nepal by air or by land.
BY AIR
Kathmandu is the only international airport in Nepal. There are a number of International Airlines with direct flights to Kathmandu.
Thai Airways International operates daily flight between Bangkok and Kathmandu.
Qatar Airways flies twice daily between Doha and Kathmandu with connecting flights to/from Europe and America.
Gulf Air flies twice daily flight between UAE and Kathmandu with connecting flights to/from Europe and America.
Etihad Airways fly daily from Abudhabi to Kathmandu with connecting flights to/ from Europe.
China southern fly daily from Guangzhou to Kathmandu with connecting flight to America Australia and Japan.
Silk Air from Singapoor fly daily with connecting flight to various country.
Indian Airlines have frequent flights between Delhi, Calcutta and Kathmandu.
Zet Airways as well as other airlines fly to Kathmandu daily from Delli India.
Royal Nepal Airlines fly between Kathmandu Delli, Kathmandu Bangkok, Kathmandu Quala Lampur and Kathmandu Hongkong.
Beside these there are Biman Bangladesh, Pakistan Airlines, Korean Airlines,connecting Kathmandu with many countries.
BY LAND:
You can go for overland travel to enter Nepal from both India and Tibet.
If you are in Tibet, you can enter Nepal by crossing the border at Kodari. Thereafter, take a bus to Kathmandu. This will take you 7 to 12 hours depending on the road conditions.
The easiest and hassle free overland route to Nepal from India is via Gorakhpur using train and the Sunauli/Belahiya border post. The only direct buses from this route to Kathmandu run at night and take approximately 9 hours. Raxaul/Birgung border post can also be used to visit Nepal. But this may not leave you with a pleasant travelling experience. If you are in Darjeeling you can come to Nepal via Kakarabhitta. There are also several border crossings in west Nepal.