Before we start, you should ensure that your mic is plugged, and that you have selected it in the Audio Settings panel.
This done, you can move your mouse over the small mic icon on the top right corner of the GLOBAL pane and you will see a popup pane appear with various settings to configure your mic channel.
First step is to check that the meter on the right side of the pane moves as you speak in the mic. If it doesn't it means the app is not receiving any audio input. Check your Audio Settings panel again, possibly deselecting and reselecting your mic in the Audio Input dropdown.
Now that you can see the meter moving, you can adjust the level of the mic so that the signal doesn't reach the top, even when singing very loudly. This will avoid that your voice "clips" which means the audio signal goes above the limit and is therefore trimmed, creating a disturbing rasping sound.
There is also a pan slider, so if you want your voice to sound a little bit to the side compared to other instruments in the session, you can play with that a bit.
Finally, you have an Effects table, where you can add effects to tailor the sound of your voice exactly the way you want.
To monitor your voice while you customize these effects, check out the section on monitoring audio input.