If you notice that the engine starts but dies soon after, then the alternator probably isn't keeping the battery charged. When you start up the car and notice that the interior lights are slowly fading, it could also indicate an issue with the alternator.
If you try jump starting the car and it works, it could imply an issue with the battery. However, it is important to note that a dead battery can also be caused by a failing alternator.
To test the starter, put on the headlights, if they don't come on, then the battery is probably flat or dead and may need to be recharged or replaced. If the headlights do come on, then try starting the car. If it still won't start, then the starter motor may be the problem.