indeed and just to spell it out
Apple Car play is for apple products such as iPhones.
Siri is for Apple.
Android has Android Auto. if your mercedes supports apple car play there is a fair chance it will support android auto as well but you are going to have to Google that for yourself.
once you add your android phone to your car, android auto should work seamlessly, mine auto connects wirelessly when my phone is near the car. yours may be wired or wireless again you need to Google it to find out
apple car play and android auto are functionally similar but are competing products
a bit like betamax and VHS
or HDDVD and Blu ray
work out which you want to use and stick with that.