Before we get started, there are a few items to be aware of. Japanese has a very limited number of sounds in the language. There are five vowels in Japanese, and each is pronounced in exactly one way. The are no "hard" vowels or "long" vowels. Each vowel is pronounced exactly the same every time. The vowels are:
|a||あ||a as in father or swan|
|i||い||i as in ski or feed|
|u||う||u as in flute or tuba|
|e||え||e as in echo or tell|
|o||お||o as in Ohio or hotel|
Every other sound in Japanese is a consonant followed by a vowel, or the n (ん) sound. Yes, n by itself is a single mora, the equivalent of a syllable in English. When you're first starting to learn Japanese, this is probably one of the most important things to understand. Every mora (syllable) is either a vowel, a consonant followed by a vowel, or n. One of the consequences of this is that every word in Japanese ends in either a vowel, or n.
The result of this system of sounds is that the Japanese cannot directly pronounce words that have double consonants in them. Likewise, any word that ends in a consonant other than n will get a vowel tacked onto it. It is nearly impossible for a Japanese person to end a word in a consonant other than n, and I've tried to teach this (without success) to Japanese people for years. For example, crayon becomes koo-ray-on when pronounced by a Japanese speaker. Black would be pronounced boo-rah-koo. It takes a little getting used to, but if you learn this simple rule from the start, your studies will be much easier. If you're just a casual learner who wants to travel a bit, this will help you better understand what someone is saying when they seem to insert extra vowels into words where they shouldn't be.
The consonants available in Japanese are also a bit limited, and this sometimes results in strange pronunciations as well. The consonants available in Japanese are K, S, T, N, H, M, Y, R, and W. There's no chart of mapping these consonants to Japanese letters, because consonants never stand alone, they are always followed by a vowel (see rule above).
Now that we understand a little about how Japanese sounds, we can come up with a system for writing Japanese words in English. (We call this method of writing Japanese with English characters Romaji.) There's one more item we need to learn about first, though, and that's the concept of double vowels. Every mora in Japanese has the same length of pronunciation. The ka sound is as long as the n sound which is as long as the mo sound. This allows Japanese to have double-length vowels, and they're used quite often. The city of Osaka is really O-o-sa-ka, four syllables. Different language books use different methods to show the double vowels. Usually we write these double vowels simply as they sound, such as ojiisan (おじいさん, grandfather), but a double O sound is a bit special. This we usually write as ou, both in English and in Hiragana, one of the Japanese "alphabets." This is the convention I'll use here, so Tokyo in English becomes Toukyou when written in Romaji.