Making database tables 1NF
You're on the right track with splitting up your domains and using a linking entity.  Separating the Films from the Stars is absolutely the first step.  


 ---------------------------    -------------------------
| FilmID |     FilmName     |  | StarID |   StarName     |
|--------+------------------|  |--------+----------------|
| EVIL01 | The Evil Dead    |  | 000001 | Bruce Campbell |
| EVIL02 | Evil Dead II     |  | 000002 | Sarah Berry    |
| EVIL03 | Army of Darkness |  | 000003 | Marcus Gilbert |
 ---------------------------    -------------------------


The missing piece is tying the two together.  Obviously, stuffing the StarIDs into the Film table is in violation of the first normal form, since you end up needing to store multiple references to actors in a single row.


 --------------------------------------------
| FilmID |     FilmName     |     StarIDs    |
|--------+------------------+----------------|
| EVIL01 | The Evil Dead    | 000001         | 
| EVIL02 | Evil Dead II     | 000001, 000002 |   Wrong,
| EVIL03 | Army of Darkness | 000001, 000003 |   Wrong
 --------------------------------------------


Splitting the offending column out to its own table restores the integrity of the original Film table, but continuing to store multiple references in a single attribute still invalidates 1NF for the data model.


 ---------------------------    -------------------------
| FilmID |     FilmName     |  | FilmID |     StarIDs    |
|--------+------------------|  |--------+----------------|
| EVIL01 | The Evil Dead    |  | EVIL01 | 000001         |
| EVIL02 | Evil Dead II     |  | EVIL02 | 000001, 000002 |   Still
| EVIL03 | Army of Darkness |  | EVIL03 | 000001, 000003 |   Wrong
 ---------------------------    -------------------------


To rectify this is fairly simple, as you merely need to associate each FilmID with the respective StarID, bringing your model in-line with the tenants of 1NF.


 ---------------------------    -----------------    -------------------------
| FilmID |     FilmName     |  | FilmID | StarID |  | StarID |   StarName     |
|--------+------------------|  |--------+--------|  |--------+----------------|
| EVIL01 | The Evil Dead    |  | EVIL01 | 000001 |  | 000001 | Bruce Campbell |
| EVIL02 | Evil Dead II     |  | EVIL02 | 000001 |  | 000002 | Sarah Berry    |
| EVIL03 | Army of Darkness |  | EVIL02 | 000002 |  | 000003 | Marcus Gilbert |
 ---------------------------   | EVIL03 | 000001 |   -------------------------
                               | EVIL03 | 000003 |
                                -----------------


Now, with the the data normalized in this manner, it is easy to add attributes to expand the model.  Say an actor's character name in a movie was desirable, you could add CharacterName to the FilmStar table - maybe useful for getting a list of everybody who's ever played "James Bond," for instance.