Mics are enabled by default. Check your audio settings. As for the other issues, please include a log file, it's most likely due to poor settings:
https://obsproject.com/forum/threads/include-a-log-file-if-you-have-a-problem-heres-how.16571/
If you are on a retina display, you may have to reduce the scaled resolution in video settings. Retinas cause the default scaled stream resolution to be a bit too high, and can be too much for some computers to encode.
Microphones can be added in audio settings. One microphone should be on by default.