つ — tsu

つ is one stroke that starts at the upper left, runs right, then sweeps back down and to the left. It sits high in the writing square, which is the fastest way to tell it apart from し.

The ts sound does not exist at the start of English words, so tsu takes practice: it is the ts of “cats” followed immediately by u, not “tuh-soo”.

The small っ is a different character

A half-size っ marks a doubled consonant — きって (kitte, stamp) rather than きて (kite, come). Same shape, different job, and the size difference is the only clue.