A hyphen (-) looks like a very short line. It is shorter than an en dash (–) and an em dash (—). It is also different from an underscore ( _ ).
On a computer keyboard, it is to the right of the zero (0) key. On a phone keypad, it is in the number menu, just underneath the “1” key.
Hyphens are used to connect words or parts of words (e.g., “self-reliant,” “semi-independent”).