Lockup Amount = Bid Amount + Added Blind
Your lockup is the sum of your bid and your blind. It's called a "lockup" because you won't be able to use your locked up HNS until the auction ends. This is to prevent people from bidding more than they can spend and to prevent people from spamming bids on more names than they're willing to actually purchase.
It's important to note that only bids determine the auctions' winners - the blinds are completely optional. Adding blinds can be helpful because they hide the value of your bid and causes your bids to appear higher to others (only you can see your bid amount while the lockup amount is what's shown to other bidders). You also receive your blind back right at the beginning of the reveal period, while your bid is you only returned once the reveal period has ended.
Your lockup cannot be updated after you submit it. You can submit additional lockups but your previous ones will still be locked up (e.g. if you submit two lockups of 1,000 HNS and 10,000 HNS, 11,000 HNS will be locked up for the duration of the auction).