The measure word 个 (ge) is the most common Chinese measure word. It can be used in a pinch for any noun if you can't think of a more precise measure word. Also, for many nouns, 个 is the only correct measure word.

General structure
The general structure for 个 (and measure words in general) is:

You can specify the quantity of any noun with this structure. Note that any time you want to state how many of a noun in Chinese, you probably need a measure word. First get used to doing it with 个.

Examples

Omitting the number
If the number is one (1), you can omit it and use 个 by itself. This is equivalent to a or an in English, for example in "a person" or "an idiot."

Some examples of that: