Below are the basic steps for using a USB mic in Studio One:
1. Go to Options > Audio Setup > Audio Device and choose Windows Audio as the audio device.
2. In that same window, click Control Panel and select the USB mic as the Recording Device.
3. Choose whatever device you plan to listen on as the Playback Device.
4. At the top of that dialog uncheck the Exclusive Mode box to avoid potential device sharing conflicts with Windows
When you create a new song in Studio One make sure to set it to the same sample rate as the USB mic. Most if not all USB mics operate at a single sample rate so if your mic only operates at 48k, make sure the Studio One song is set to 48k in Song Setup > Sample Rate or in the new song dialog.
You probably also want to make sure that the USB mic is not the default recording device in Windows Control Panel > Sound > Recording, to avoid any potential conflicts trying to use it it in Studio One and if you do run into any issues, select it there and click Properties > Advanced and uncheck Allow applications to take exclusive control of this device.