Passing Record Info to Code Pages

Your two primary options will be the currently logged in user or URL parameters. 

So in your example - if you're querying data and it's specific to that user, you can amend your query to include something like: {'4'.TV.'_curuser_'} as an example of grabbing records where the record owner is the currently logged in user. 

Alternatively and more specific to your description - lets say you're launching a job summary page for a specific job - you can have a button where you include URL parameters in the URL string to launch the interface through a button with the data you need like:  

https://realm.quickbase.com/db/appid?a=dbpage&pageid=PAGE ID&jobRid=[Record ID#]

You can include as many params as you need and then just code in the handler for each param to assign as a variable for the other bits in your code.