Do you have any specs?
The LM386 is a "power amplifier, designed to drive a speaker.
A "normal" audio signal is AC. It goes positive an negative, and negative voltages can fry your Arduino... Especially from a power amplifier (with enough current-capability to drive a speaker).
Also, electret microphones need "power". Laptops, soundcards, and phones provide 5v out to the microphone, but most mic preamps don't.
Most "sound sensor" boards (like this) have a biased output. The output rests at 2.5V and with silence you get (about) 2.5VDC and a regular Arduino with a 10-bit ADC reads 512 (with silence).
The AC audio signal "rides on top" of the DC and goes up & down from there. The louder the sound, the more the positive & negative peaks deviate from 2.5V. (You can easily subtract-out the bias in software if you wish.)
P.S.
If you can use a line-level audio signal (like the RCA outputs on a CD/DVD player, etc.) or a headphone signal instead of a microphone, there is a schematic for a bias circuit in my post for The World's Simplest Lighting Effect.
Do NOT connect a speaker wire! Depending on amplifier power, you might get too much voltage and again, fry the Arduino.