Rōmaji (ローマ字) is the writing of Japanese in Latin, the same alphabet used in English.
There are several different spelling systems for Rōmaji. The three main ones are:
Variants of the Hepburn system are the most widely used. Here is the most common Rōmaji alphabet using the Hepburn system:
A B CH D E F G H I J K L M N O P R S SH T U W Y Z
(The Hepburn system is based on English spelling, and doesn't use C by itself, Q, or X)
The long vowels are generally indicated by macrons ( ¯ ), and every consonant must be followed by vowel except for the letter N.
Here is an example of Japanese text in Hepburn Rōmaji:
"Subete no ningen wa, umarenagara ni shite jiyū de ari, katsu, songen to kenri to ni tsuite byōdō de aru. Ningen wa, risei to ryōshin to o sazukerarete ori, tagai ni dōhō no seishin o motte kōdō shinakereba naranai."
Japanese has 4 writing systems (5 if you count numbers as a writing system):
Japanese keyboards are usually set up like an American or European keyboard. You type in a word in Rōmaji, and the computer will automatically come up with the hiragana or katakana. You then press the spacebar and it will convert the previous word into kanji that you want. You don't convert every word; only certain words are spelled with kanji characters.