What the cent sign means
The cent sign ¢ stands for one hundredth of a dollar, so 25¢ is a quarter and 99¢ is just under a dollar. It is a small c with a vertical or slanted line through it; both styles are the same character.
The sign goes after the number with no space: 5¢, 50¢. Once an amount reaches a dollar, switch to the dollar sign with decimals ($1.25, not 125¢). Never use both in one price: $0.99¢ technically means 0.99 of a cent, a common mistake on signs and menus.
Many typewriters had a ¢ key, but standard computer keyboards dropped it, which is why so few people know how to type it today. It still appears on price tags, in store names and in math word problems.
Cent sign vs. look-alikes
A few characters look like a cent sign but mean something else. ₵ is the cedi sign, the currency of Ghana, and ₡ is the colón, used in Costa Rica. ȼ is a Latin letter c with a stroke, not a currency sign, and ©︎ is the copyright symbol. The fullwidth ￠ is the cent sign sized for Chinese, Japanese and Korean text. Every other money sign is on the currency symbols page.
How to type ¢
On a Mac, press Option + 4. On Windows, hold Alt and type 0162 (or 155) on the number pad with Num Lock on. In Microsoft Word, you can also type 00A2 and press Alt + X.
On iPhone, open the 123 keyboard, press and hold $ and slide to ¢. On Android, Gboard has ¢ on its second symbols page: tap ?123, then =\<. In HTML, use ¢, and in LaTeX use \textcent from the textcomp package.