Text styles can be applied to text within your publication for efficiency and consistency.
A text style is a set of one or more text attributes which can be applied to text in bulk. An attribute could be a typeface, trait (bold, italic), font size, spacing, alignment to name only a few. Later, if you chose to modify a text style, any text which uses that style will update to conform to the attribute changes you've made.
Every new document comes with a default set of text styles but the Text Styles panel provides you with the ability to create and manage a document's text styles as well as remove them.
Text styles can be applied to text using the Text Styles, Paragraph or Character panels, the context toolbar or a custom keyboard shortcut.
Local formatting means that you apply a text attribute(s) directly to a character, word or paragraph. These settings are not stored so if you want to do the same to other text you'd have to do it all again. This is fine for smaller passages of text but for longer publications this might be laborious and also create inconsistency. Character formatting overcomes this by saving those attributes to a named character style that can be applied to any text just with one click. When working with paragraphs, you can adopt paragraph styles using the same principles as character styles.
If you have a mix of local and character formatting on a paragraph, and you apply a different paragraph style to that paragraph you can control the override behaviour of local and character formatting, i.e whether it is removed or kept.
Two additional Apply <style> to Characters options let you apply a chosen paragraph style as a character style to selected text—either removing or retaining any local formatting on selected text.