Hopefully this will make sense.
Say I have a website called www.test.com (it probably exists but I am making all the URLs up for this post).
I have a second website called www.oldsite.com.
I want to have the website www.oldsite.com to point to a page on www.test.com so if you go to www.othersite.com in your browser you get redirected to www.test.com/newsite.
I know how to get the domain pointed to the right server (update DNS). I also am aware you can redirect people who hit www.test.com to www.test.com/newsite.
What I want though is for people who type in www.test.com to land at www.test.com and people who type www.oldsite.com to land at www.test.com/newsite.
How do I do this?