Need help with Japanese...this has got me so confused.?

The simple answer is that it's just a convention of the Japanese language.

Here's an answer I gave on this same topic a few years ago (check sources for a link to another similar question with an answer that might also be helpful and a link to a Wikipedia article on the sokuon):

That "little tsu", (note the size difference that it's ッ not ツ) is called a 促音 ("sokuon") in Japanese. It's pretty much used whenever the word requires it to be used. What it does is double the first consonant of the next kana that follows it creating a very slight pause when you speak the word.

Eg: っか (kka), っす (ssu), って (tte).

けっか (kekka)

おっす (ossu)

ひっこす (hikkosu)

いって (itte)

One other use you may see for the small tsu, is at the end of a word, usually in katakana. This causes the word to finish on a hard sound rather than pronouncing the vowel of the final kana. An example of this can be found in the title to the anime Chobits. In Japanese, it is written as ちょびつッ. The ッ is what causes it to be pronounced as "Chobits" and not "Chobitsu".

To type it, just type the romaji with the reqired double letter and it will automatically recognise it. The "retto" part should come out as レット. If you're using the Microsoft IME to type Japanese characters, you can type "ltsu" without the quotation marks to generate a half size "tsu".