The <title> tag is a HTML element that browsers and search engines use to determine the title of a given page.
You would typically be using a phrase built around one or more of your most valuable keywords, likely along with your brand or site name.
<title>Web Design, Ads, SEO Agency Southampton • Northrook</title>
Note: Most search engines, including Google and Bing, have a limit on how long of a title they're willing to display. This is typically around ~60 characters, or a pixel length of ~560px. Good SEO tools for WordPress (like SEOPress and Rank Math) will let you know if you exceed either.