You will need good soldering skills to successfully assemble this kit - due to the small physical tolerances between adjacent traces on the solderable breadboard used as its base.
The audio input port of modern computers normally requires a "modern" microphone (powered electret or condenser microphone) to work properly. But what about those high quality, heavier, and better sounding dynamic microphones you have lying around from decades ago (or that you can pick up at garage sales)? Those won't work (directly) with your computer because they cannot provide enough "drive".
This kit is a one-stage transistor amplifier that has a phone jack input (to accept that dynamic microphone) and an 1/8" stereo plug output (to plug directly into the "mic" audio port of your computer). It provides a little bit of amplification and a little bit of impedance matching - so your dynamic microphone can now work just fine with your computer, and you get excellent audio out of the deal, too. You can also learn a little about how transistor amplifiers work. Power is provided by a 9V battery, and it is built on a small printed circuit board. (Provides single-channel output.)
A power switch is included as well as an LED to help remind you to turn it off and save the battery when it is not in use.