Preference settings to record a mix - help please!!!

Hi, I’m trying to record a mix from my mixer but can’t find any help for audacity latest version 2.3.0 on mojave os 10.14.3. Any help will be really appreciated!! I’ve connected rca from mixer to my microphone input on mac but cant figure out the preference setting on audacity to start recording. Thanks in advance for your time!!!

my microphone input on mac

Which Mac?

Unless you have a Mini with “real” stereo inputs or an older Mac…

…you’ll need a stereo USB adapter such as the Behringer UCA-202


Which mixer? The mixer could have USB connections.