Title tags, in the simplest terms, are the names of your website pages. You know when you open a bunch of tabs on your web browser and each tab has a little bit of text? That's essentially what a title tag is.
Just like you'd name a file on your computer so you can find it easily, you want each page of your website to have a clear, descriptive title. This way, both people and search engines (like Google) can understand what your page is about right off the bat.
Imagine owning a bakery and having a website for it. A good title tag for your contact page could be "Contact Us - Marie's Bakery", while for your menu page, it could be "Menu - Marie's Bakery". The title tag gives a quick snapshot of what to expect on the page.
Title tags aren't just important for humans. They're a critical part of how search engines understand your website and determine where to rank it in search results. The more relevant and descriptive your title tags are, the more likely it is that your website will appear when someone searches for a topic related to your business.