So for example this site, security.stackexchange.com, when I look in my browser it doesn't say that it uses https and it does say that my connection is not encrypted. The same goes for, say, twitch.tv.
When you log in to this site, security.stackexchange, it does say that it uses https, but when I'm just browsing the site it says it doesn't use https. Is this secure? If it is, how? Aren't headers and cookies (like session id) and all data in my requests unencrypted and vulnerable to attackers every time I request a new page?