A USB audio interface converts the analog signal from a microphone into a digital signal your computer can understand. They come in many shapes, sizes and prices. For what you are doing, you don’t need to spend a ton of money but don’t cheap out. Cheap, off-brand interfaces can introduce buzzes and other noises into your audio. They also don’t last as long. Among decent interfaces, price is often related to the number of possible inputs.
If you are only planning on using one microphone, this little box is all you need. Behringer makes decent products. You could spend 10 times as much but, likely, in recording a podcast, you wouldn’t be able to tell the difference. This has a built-in preamp to raise the level of your microphone high enough to get a clean signal and phantom power in case you need to power your microphone.
Cost: $29 (Amazon)
Connection: XLR, 1/4″
Behringer U-Phoria UMC204HD If you want to add an additional microphone, this unit is basically the same as the UM2 just with 2 microphone inputs both with preamps and phantom power.Cost: $79 (Amazon)
Connection: XLR, 1/4″