How http proxy clients work

if an HTTP client reaches a website through a proxy (not reverse proxy) server, what are the actual HTTP request and its parameters that are sent from this client host to the internet?

for example: Proxy Server: www.proxy.com:80 Target website: www.website.com:8081

Does the HTTP client send the following Get request?

Get http://www.proxy.com:80 Host: www.proxy.com:80

OR Get http://www.website.com:8081 Host: www.proxy.com:8081

if the first case is true, How can the proxy know what is the actual destination to forward this request?

otherwise, if the second is true, how can the request actually reach the proxy host machine?