Well the echo really depends, are you watching your stream while you're streaming? If so, mute it because OBS picks up any sound on your computer. As for the microphone, once it is plugged in and working you just go to the "Audio" section in settings and there should be a drop down next to Microphone/Auxiliary Audio Device where your mic will be listed (try clicking reinitialize if it isn't showing in the list). Also make sure to check "Force Microphone/Auxiliary to Mono" so your mic isn't only in the left or right channel. Hope that helped and good luck streaming! :D