When working with HTML, it's important to understand the difference between block-level and inline elements.
A block-level element defines a section in a document that always starts on a new line and takes up the full width available. On the other hand, an inline element also defines a section but does not start on a new line and only takes up as much width as necessary.
It's crucial to note that you cannot place a block-level element inside an inline element due to their different display behaviors.
In HTML, there are two main types of elements: Block-Level Elements and Inline Elements. Examples include div for block-level and span for inline elements.