ok... since I have a Japanese word processor and just expressing in words sometimes is confusing, I will show you what they mean (btw... you need to have Japanese character set loaded on your computer to see the characters)
tsu makes a dubble consonent by writing it smaller before the double consonant:
-in the word "motte" (meaning have) もって
-in the word "kappu" (meaning cup) カップ
To make a vowel long in kana (the phonetic system of writing) you simply add a "macron", a dash after the vowel or write it out using u with u and o or doubling "aa", "ii", and "ee":
-in "douzo" (by all means, please) どうぞ
-in "ee" (yes) ええ
or
-in "sa-bei" (survey) サーベイ
I hope that helped, I'm not the best teacher but I try.