You should have your api keyset (two keys) ready. If not, generate them. These tokens are tied to your account, and thus, to your identity. Like all API keys, these are of course NON-TRANSFERABLE and should never be communicated to third-parties (and I won't call you and ask them either).
With these two keys in hand, you'll then need a request. Let's just issue a PUT on /users/test_user with "github=testgithub". In curl this should look like this:
$ curl -X PUT -d "github=testgithub" http://api.techshaker.com/users/test_user
Well, not really, we also need to authenticate. Authentification is done by adding your API_KEY ("the short one") to the headers as "X-API-KEY". Like this:
$ curl -X PUT -H "X-API-KEY: YOUR-API-KEY" -d "github=testgithub" http://api.techshaker.com/users/test_user