A paragraph consists of one or more sentences. Though not required by the syntax of any language, paragraphs are usually an expected part of formal writing, used to organize longer prose. The oldest classical Greek and Latin writing had little or no spaces between words or other ones, and could be written in boustrophedon.

Greek paragraphos
Brief Specfification
The oldest classical Greek and Latin writing had little or no spaces between words or other ones, and could be written in boustrophedon (alternating directions). Over time, text direction (left to right) became standardized, and word dividers and terminal punctuation became common. The first way to divide sentences into groups was the original paragraphos, similar to an underscore at the beginning of the new group. The Greek paragraphos evolved into the pilcrow, which in English manuscripts in the Middle Ages can be seen inserted inline between sentences.
The History of Paragraphos
In ancient manuscripts, another means to divide sentences in into paragraphs was a line break (newline) followed by an initial at the beginning of the next paragraph. An initial is an oversize capital letter, sometimes outdented beyond the margin of text. This style can be seen, for example, in the original Old English manuscript of Beowulf. Outdenting is still used in English typography, though not commonly. Modern English typography usually indicates a new paragraph by indenting the first line. This style can be seen in the (handwritten) United States Constitution from 1787. For additional ornamentation, a hedera leaf or other symbol can be added to the inter-paragraph whitespace, or put in the indentation space.
A second common modern English style is to use no indenting, but add vertical whitespace to create “block paragraphs”. On a typewriter, a double carriage return produces a blank line for this purpose; professional typesetters may put in an arbitrary vertical space by adjusting leading. This style is very common in electronic formats, such as on the World Wide Web and email.
Paragraph Examples
“Lorem ipsum dolor sit amet, consectetur adipiscing elit. Elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo. Luctus nec ullamcorper consectetur adipiscing ipsum dolor sit.”
“Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo. Luctus nec ullamcorper consectetur adipiscing ipsum dolor sit.”
“Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec llamcorper mattis, pulvinar dapibus leo. Luctus nec ullamcorper consectetur adipiscing ipsum dolor sit.”
A second common modern English style is to use no indenting, but add vertical whitespace to create “block paragraphs”. On a typewriter, a double carriage return produces a blank line for this purpose; professional typesetters may put in an arbitrary vertical space by adjusting leading. This style is very common in electronic formats, such as on the World Wide Web and email.
In ancient manuscripts, another means to divide sentences in into paragraphs was a line break (newline) followed by an initial at the beginning of the next paragraph. An initial is an oversize capital letter, sometimes outdented beyond the margin of text. This style can be seen, for example, in the original Old English manuscript of Beowulf. Outdenting is still used in English typography, though not commonly. Modern English typography usually indicates a new paragraph by indenting the first line. This style can be seen in the (handwritten) United States Constitution from 1787. For additional ornamentation, a hedera leaf or other symbol can be added to the inter-paragraph whitespace, or put in the indentation space.

Hello world!
Welcome to WordPress. This is your first post. Edit or delete it, then start blogging!
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras vitae venenatis felis. Cras vitae facilisis nunc. Nullam bibendum varius odio non varius. Pellentesque eget hendrerit lacus, eu commodo ante. Proin iaculis cursus eros, ac molestie ipsum blandit ut. Suspendisse potenti. Nunc cursus, ex sit amet tempor aliquet, enim lacus fermentum sapien, eu condimentum ex elit sed nisi. Pellentesque vitae dui tempus, tempor felis quis, placerat orci. Donec vehicula metus dui, sit amet finibus nunc imperdiet sit amet. Suspendisse eget justo tincidunt, pellentesque sem pulvinar, mollis erat. Nullam vestibulum rhoncus tempus. Nullam sollicitudin eros ipsum, quis facilisis felis convallis sed.
Duis eu pharetra lacus. Sed felis arcu, posuere quis interdum in, molestie eu nulla. In vestibulum congue ante nec molestie. Nunc lectus diam, fringilla ut pellentesque vitae, faucibus ut nisl. Nunc consectetur aliquam molestie. Aenean et odio eros. Praesent nec lectus vel felis finibus suscipit. Mauris eget dictum dui. Nulla vulputate diam non purus congue, a varius diam egestas. Proin a efficitur enim.
Phasellus nec venenatis augue, sed feugiat lectus. Cras dolor est, porta a consequat quis, eleifend ac ex. Etiam facilisis augue placerat sagittis convallis. Sed id laoreet urna. Vestibulum condimentum turpis nunc, at mollis quam mattis laoreet. Quisque in efficitur leo. Vestibulum faucibus diam sed metus malesuada blandit. Sed vel mi sit amet lorem interdum ullamcorper. Vestibulum in lobortis metus. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque mi mauris, mollis in tempus eu, sollicitudin vel tortor. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Vivamus ut maximus purus.