The tilde ( ~ ) can be many things, such as a diacritic. Many languages use tildes. Two of these are Spanish and Portuguese.
In Spanish, the tilde, which is only put over the N ( Ñ ), makes it sound like [ɲ] (like 'ny' in canyon) instead of [n].
The tilde also appears in Portuguese where it is used to nasalise (meaning to sound them through the nose) the vowels "a" (ã) and "o" (õ).
In UNIX operating systems, a tilde represents the user's "home" directory.
The tilde is also used to denote when something is an estimate, such as ~24 meaning approximately 24.
On most QWERTY keyboards, you can type a tilde by holding down the shift key and pressing the "`" (single back quote). This key is in the upper left corner of the keyboard, below the esc (escape) key and to the left of the key that you use to type the number 1 or an exclamation mark (!).
Wikipedia editors sign their comments on Talk pages with four tildes (~~~~).