<title> tag allows defining the titles of web pages. This title is the part that is seen on the tabs in the browser. Also, title tag defines the title on search engines.
As can be seen on the image, title and description parts appear in search results. The blue part on the top shows the title of the site whereas the bottom part shows the description of the site. This is why title tag is crucial for search engines.
<title> tag is used between head tags; and its usage is as follows.
<html> <head> <title>Title</title> </head> <body> </body> </html>