Not in every company you can access sites like github.com as easy. Sometimes you may sit behind a proxy. In addition you may also have internal git repos which you need to access. In that case best way to do so is to define a proxy for github.com in your gitconfig file

[http]
	sslcainfo = /ssl/certs/ca-chain.pem
	sslBackend = schannel
	proxy=
[http "https://github.com/"]
	proxy=http://{username}:{password}@{proxy-server}:{port}

In case you are running git on windows and authenticate by ntml you can leave username and password empty. So the url looks something like http://:@...

proxy=http://:@{proxy-server}:{port}

Credits: https://stackoverflow.com/questions/1783659/does-git-clone-work-through-ntlm-proxies