An audio interface converts microphone and instrument signals into something a computer can record, and converts the computer's output back into sound you can hear. That is the whole job.
Preamps
Microphones produce a very small signal. The preamp raises it to a usable level. Clean preamps with enough gain matter most if you use dynamic microphones, which need considerably more amplification than condensers. Insufficient gain is the usual reason a recording is noisy.
Phantom power
Condenser microphones need power supplied down the cable, usually labelled 48V. Dynamic microphones do not need it and are not harmed by it on a standard balanced connection, though it is good practice to switch it off when unused. Always mute before switching it on or off.
Inputs and outputs
Count the sources you will record at the same time, then add one. Two people in a room needs two microphone inputs. A four person video podcast needs four. Outputs matter for headphones: if three people need to hear a mix, you need enough headphone outputs or a small headphone amplifier.
Separate tracks
The reason to use an interface rather than a mixer with a single stereo output is that each microphone can be recorded as its own track. That one decision makes editing and balancing dramatically easier.
Latency
Latency is the delay between sound going in and coming back out of your headphones. Most interfaces offer direct monitoring, which routes the input straight to the headphones with no delay. Use it when recording vocals; it is the difference between a comfortable performance and an unsettling one.
Sample rate and bit depth
Recording at 24 bit is worthwhile because it gives room to record conservatively and raise the level afterwards. For voice and most music, 48 kHz is a sensible standard and matches video workflows. Higher rates fill drives faster with little practical benefit for speech.
Connections and power
Check the connector your computer actually has, and whether the interface is powered by the cable or needs a separate supply. Bus powered units are convenient for location work; mains powered units often deliver more gain.
Do not overbuy
A reliable two or four input interface will serve most podcasts and home studios for years. Spend the difference on treating the room.