Here's a more thorough explanation and the examples of this 'alphabet.'
Rōmaji was developed to describe the sound of Japanese in Roman (Latin) alphabet and it's mainly used for the convenience of foreigners who are not familiar with Japanese characters.
Rōmaji is used, more often than not, alone. It's not mixed with other Japanese characters.
There are different ways of spelling, but the Hepburn Romanization is the most common style used.
How to Read Rōmaji
Basically, you can read Rōmaji as you usually read English texts, BUT the pronunciation of Japanese syllables is not exactly the same as English.
Irregular spellings are colored in red.
NOTE: For all of the pictures that follow, the hiragana will always be on the left and the katakana will always be on the right. Example: か / カ
The next table shows the Yōon letters (pronounced You-on). These combine the 'y' with the other kana letters to create more sounds.
...And the last two tables show us how to have a double consonant and long vowels.