You can immediately identify a paragraph by the way it looks. Not that you should generally judge things based on their appearances, but most paragraphs won’t be too offended.
A paragraph is a collection of sentences that is separated from the rest of the text by spacing and/or indentation. Or, if they’re especially aggressive, by a bouncer.
A paragraph usually focuses on one idea or theme or subject. It clearly states this idea up front in a topic sentence, and then develops it with support and examples. Some paragraphs also have a concluding sentence or sentences that summarize the contents of that paragraph. So if the rest of the paragraph ever gets lost, authorities can step in and attempt to locate it.