Long vowels are handled differently in katakana compared to hiragana. Instead of adding extra vowels to extend the sound, katakana uses a simple dash-like symbol: ー This symbol tells you to lengthen the vowel sound of the character it follows. For example:
サカ (saka) becomes サーカー (sākā, soccer)
ノト (noto) becomes ノート (nōto, notebook)
The sound is smooth and continuous, not repeated, making it an important part of writing foreign words or names in katakana!