Assuming you'd prefer to diagnose the starter before just replacing the part, please provide a bit more detail. When you turn the key to the Start position and hold it there for a couple of seconds do you get a single click, a single click followed by a series of clicks, or a rapid sequence of clicks.
If you get a solid, fairly loud single click, the problem is likely in the starter assembly. If you get a series of clicks, that typically suggests the problem is due to low voltage to the starter and starter solenoid. That could be a weak battery and/or dirty connections or cables. If you get a single rather quiet click your PCM relay may be engaging but not the starter relay. That could be an issue with the Digital Transmission Range Sensor (another common issue). For that you might try shifting to neutral and trying to start it again.
-Rod