Audio interface is an external sound card that converts from audio/digital and vice versa and will hook to the laptop vis usb (pretty sure yours doesn't have firewire). Depending on the unit, it may also include preamps, processing, outputs for powered speakers, etc. Usually has mic or instrument level inputs.
Your laptop has an onboard soundcard (i.e., realtek, etc.). The onboard card may do the trick no problem. If you have an external soundcard, you likely won't need the DI. Although, there is much to be discussed there as well. But that's for another time.
