I don't understand the Japanese character "ツ "?

I've been learning Japanese and understand the different characters for hiragana and katakana, and I get that ツ is "tsu" but what I don't understand is how the word shopping (in romaji "shoppingu") turns into ショッピング. Doesn't that say sho (shi+yo) tsu pi n gu? Or is ッ a different character than ツ?