hmmm - okay - i might miss something here but i try to share what i know
calling it “the db” feels kind of strange to me - thought it of course is a huge db …
when accessing safenet via your app you have access to files (private / public) and you can create folder & files “in your account” - make folders public and share them with others
it means that you only can store and retrieve data from safenet - there is no direct messaging between 2 safenet-users supported yet and there is no payment (safecoin and transactions)/farming implemented into the protocol
if you want to create a stand-alone app without any data-sharing with others you program your GUI, take the data you want to process - validate it - and store it in your private safe folder (probably you’ll want to create an app folder first there 
) after that you can read your private data and retrieve that data-file again and use it for whatever you want
maybe having a look at the codebase of safeshare
might help you to see how data can be managed inside safe via JS