There are multiple different types of business letter formats, including block and indented formats, as described by The Writing Center at the University of Wisconsin - Madison. The block format uses a simple layout with "blocks" of text that have no indentation, meaning that all sentences in a paragraph or text block line up evenly on the left and right sides.
By contrast, the indented format for business letters uses indentation of about a half-inch for the first sentence of each paragraph, according to The Writing Center at the University of Wisconsin - Madison. All other blocks of text, such as the address blocks at the top-left and right sides of the page, use no indentation. Overall, business letter formats are simple, using the same basic structure that includes several short body paragraphs.