You can buy from here: https://selly.gg/p/da30ae34What is MSDN Admin?Basically with MSDN Admin, you can claim Microsoft Keys and of course, there's a key limit for each product and account. The MSDN Invite let's you create a brand new account from where you will receive 5 more invites. That being said, you will get your account and after this you can make 5 more accounts, or you can sell the invites, just like me. Also there's Microsoft Azure and many more other tools. Which means you'll receive $150 monthly Microsoft Azure Credits per account till subscription ends which is about 3 years. Please note that the Microsoft Azure can only be used for Development/Testing purposes.
MSDN means Microsoft Developer Network.
What is required when using MSDN Admin?Nothing is required, you just need to have an email address when sending invitation from your admin when accepting the BizSpark Invitation.
You said there's limit, how many keys can I claim?Yes, there's limit for each account. For instance 5x 8.1 Pro, 2x 7 Ultimate, 2x Pro Plus 2013 and 1x 7 Enterprise. 4 Accounts means 25x 8.1 Pro, 10x 7 Ultimate, 10x Pro Plus 2013 and 5x 7 Enterprise.