This is a pretty normal thing to to in Ignition, and it’s fairly straight forward.
To auto-populate fields, simply bind them to an expression or a non-polling query that provides their initial value. (The username could be gained using a runScript expression).
Populating dropdowns is a simple matter of binding their dataset property to a query that returns the appropriate options.
And then the button to commit the form would be written as an actionPerformed script that gathers all of the fields and then runs a system.db.runUpdateQuery command passing in the field values as query parameters.
Let us know if you get stuck anywhere.