A page title is a clickable headline that appears in the SERPs for a specific page on your website. It is the most visible part of the SERP snippet and has a big impact on your CTR, SEO and social sharing.
To set it yourself you need to use the title tags in your HTML source code. If your title is too long, Google’s algorithm will try and find an appropriate one itself. So, it is a good idea to stay under 487px for the mobile and 568px for the desktop.