You’re certainly already acquainted with document editors, like Microsoft Word, with which you can structure your document with titles, paragraph, lists, tables, images, bold and italic text.
HTML provides roughly the same elements of formatting. The key difference is that formatting text in Microsoft Word is visual, whereas HTML code is purely semantic: you provide meaning to your text.
The same way you use ♫ notes ♬ to write music, you use HTML to write webpages.