1) The name you see is not name of the file. When the file was first created from the Excel file, the table was given the same name as your file, but subsequent file name changes will not rename the table. You'd need to switch over to manage | Database | tables to rename the table. And your original layout for that table is also given the same name as this table. It can be renamed in Manage | Layouts or Layout Setup...
2) And where do you see that? Any layout can be modified to include the fields you need it to have. You can enter layout mode and use either the field tool of the field picker (new tool in FileMaker 13) to add fields to the layout. Or in table view, you can click the modify button and add fields to the view without adding them to the layout if you wish.
3) One DB is NOT a table. Open manage | Database and you'll find the tools for adding more tables to your file on the tables tab and more Tutorial: What are Table Occurrences? (not the same thing) on the relationships tab.
Final paragraph question:
It sounds like you put each table into a different file. From Excel files, this is easy to do by doing a drag and drop of the excel files onto the FileMaker application or by using Open from the File menu, but this is not ideal--especially for people new to FileMaker. It would be better to select one of your converted files and use Import Records with the "new" option selected for the target table to import the other file's data directly into new tables in the same file. Then you can go to Manage | Database | Relationships and define the needed relationships to make this a relational database. (This can be done with one file in each table, but that starts you out, as a new developer, with a more complex approach for getting the same set of tables to work as a relational system.)