Your question is a bit unclear - I can't tell if you mean 1. "how do I change records in a table through a form", or if you mean 2. "how do I put these changed records from 3 tables into a new table?"
If you meant #1, then you should be able to change records in multiple tables on a form (through a query), depending on how your table relationships are set up. You might need to fiddle a bit in the query changing and making new table relationships (called "ad hoc" relationships, since the relationship will only be present for this particular query. If you want relationships to stay across the database, then open your Relationships window by clicking the button or going to Tools->Relationships from the main Database Window.)
If you meant #2, then you can use an Append Query, set to run via Macro or DB code in the After Update event of your form. There's been a fair amount of recent discussion about it - search these forums for Append Queries for more info.