A "style" is a collection of "properties" with a name, and a style can be applied to any text to control its properties.
Understanding "styles" which is a central concept in Word makes your document-processing life easier, and your use of Word more effective.
Create a new document with some text.
Look for the sub-section "Styles" in the "Home" tab.
Select some text and then choose a style.
The text will change format according to the style.
Try the styles "Heading 1", "Heading 2", "Heading 3".
You can accept the default styles in Word, you can create your own styles, or accept the styles in any "template" document you are given.
Quick use of a style
Type some text and make it a "Heading 1" style using the special key-shortcuts. (Shift+ALT+RIGHT ARROW) or (Shift+ALT+LEFT ARROW)
Question for consideration:
When you press "enter", the next line is often in "Normal" style.
Why?
How could you change this?