I've never used the MSGEQ7 but I've studied it a bit...
The manufacture's datasheet is always the best place to start.
The output (pin 3) is analog so it needs to go-to an Arduino analog input.
Probably the key to understanding the MSGEQ7 is the timing diagram which shows you how to use the Reset & Strobe inputs. They are both active negative-edge triggered.
The cycle starts with both inputs high and then you write a low to Reset and hold it low.
After a delay, write a low to Strobe and the Analog output represents the 63Hz band.
When you're ready, write a high to Strobe. Then low again. Now, the analog output represents the 160Hz, band.
After you're done with all 7 bands, start-over again with a new reset.
There are some minimum times so everything can get set up.