I've seen the first link. These responses don't seem to be written in simple English for the simple mind. People like this kind of make me want to learn a lot about technology because then I am sure I could make simple English explanations once I actually understand what they are talking about.
I understand, It's just that the way it works itself is complicated, As HTTPS proxies may mean 3 different things, Which are:
#1 - a proxy which knows the "CONNECT" verb and is able to forward connections to a ultimate SSL-powered target server;
#2 - a proxy which is itself a SSL server and will engage in SSL with the client, to protect requests and responses when they transit between client and proxy.
#3 - Both, the proxy server is an SSL server and you will connect to it after you install a self-signed cert so that the content between YOU -> SERVER is encrypted, Also knowns the "CONNECT" protocol which will be tunneling requests between YOU -> PROXY -> HTTPS SERVICE
So if with a HTTPS proxy the browser to proxy server connection is encrypted
encryption of your data from browser to proxy is only applied if the connection to the proxy was made in HTTPS as the proxy server itself runs an ssl server. See point #2.
does that mean the proxy server to website connection is also encrypted?[
Proxy Server to website encryption is what most of the HTTPS Proxies being sold are doing which is basically making a tunnel between you, proxy and ssl-powered target server which means the proxy here sits on the middle of the request but not able to intercept it. since the ssl is being tunneled and verified. to be able to intercept it or read it the proxy server must send you a "fake" ssl cert for domain.com that you install on your device, because that's how SSL works the proxy server can't intercept SSL content for domain.com since it doesn't have the certificate validating its ownership of domain.com.
Or does a HTTPS request from the browser go through a HTTP tunnel to the proxy server and from the proxy server to the website it becomes encrypted? Wouldn't that mean that I would be sending data in plain text to the proxy server?
You can't convert HTTP to HTTPS. if you are sending data in plain-text to HTTP proxy server only you wouldn't be able to open HTTPS sites. since the request were made in HTTP beforehand. nor the proxy server has the valid certificate for domain.com to open a valid SSL connection and intercept your data.
VPN's are completely different?
it's same concept if proxy/vpn server intercepted HTTP plain-text data then created a valid ssl connection to the target server they wouldn't be able to reply back with a valid HTTPS response/website. and the secure connection to target would fail by then.
Also, is it possible to use an SSH SOCKS proxy / tunnel with different browsers? Or is that thing for the whole system?
an SSH Tunnel in simple words is a proxy. your are tunneling all requests from your current application using the proxy (i.e browser) to -> SSH connection sending it to server to handle the request for you then forward the response back to you. Also yes it can be used for whole system in some situation by setting up a forwarding rules in your machine using iptables for example.
Hope i've made it clear enough.