What are introductory phrases?

Could you please elaborate on what exactly introductory phrases are? Are they specific types of sentences or words that are commonly used at the beginning of a paragraph or conversation? How do they help set the tone and context for what follows? Additionally, could you provide some examples of introductory phrases that might be used in different situations? It would be greatly appreciated if you could break down the concept in a way that's easy to understand for someone who might not be familiar with the term.