Generating accurate and powerful bass sounds requires a lot of energy and a particular kind of speaker. It is easy for low tones and notes in music to become distorted in ordinary speakers, especially when you turn the volume up. To get a true bass, you want to invest in a subwoofer speaker, designed specifically for such low frequencies.
A subwoofer for car use needs certain components to reproduce low sounds well: an enclosure and an amplifier. The box enclosure creates greater resonance, and the amplifier increases the power of the audio signal. Some subwoofers come with one or more of these components already in place. For instance, an enclosed sub comes pre-mounted in an enclosure box. A powered sub is a subwoofer with integrated amplifier.
If you want to select each car audio component individually, choose a component subwoofer, which is just the speaker. Then you can select a compatible enclosure and connect your subwoofer to a car amplifier.