Not sure I understood what is what lol---
ChipMixer allowes certain amount to be mixed like said above; 1,2,4,8.... mBTC which allows you to filter the probable ChipMixer users by getting all the addresses containing the same amount of input.
I'm not sure how to use Chipmixer, should not be that difficult though.
Visit-
https://chipmixer.com/faq, I guess this will help you understanding how ChipMixer works.
How is using VPN affecting security?
Use TOR browser and onion address-
http://chipmixerwzxtzbw.onion/That's enough for being secured from tracking data by the website which is unlikely though.