Word tries to be helpful by automatically applying formatting to your document based on what you type. One example of this is when Word automatically creates a numbered or bulleted list for you when you enter some text that Word thinks should be a numbered or bulleted list.
When you type a number followed by a period and then press the Space Bar or the Tab key, Word automatically formats the paragraph as a numbered list. When you type an asterisk (*) and then press the Space Bar or the Tab key, Word automatically replaces the asterisk with a bullet and formats the paragraph as a bulleted list. You can cancel automatic formatting for the current paragraph by immediately pressing “Ctrl + Z” right after the automatic formatting is applied.