How to redirect from HTML page to another domain using login credentials

Can any one explain me about how to redirect the page to other domain using the login details
for example i have created a simple login page with username and password when i click on the submit button it is redirecting to the other domain login page, how can i login to the other domain home.
for example i have to the login details like> URL and username: demo123
password : demo123 for that i have created a login web page in the created login page if i give the details above it has to redirect to the dotnetspider website. can any one explain me about it with the example.