HTTPS is the secure way a browser and a website exchange information. It is like putting a letter into a sealed envelope so other people along the way cannot easily read or change it.
When a site uses HTTPS, the browser can protect information such as sign-in details while it travels to the site. You can often see this in the address bar.
HTTPS helps protect the connection, but it does not guarantee that a website is honest or that every action is safe. Check that you are on the website you intended to visit.