It's easy to record your own voice with FlexClip.

In the Media part, click the Record Voice button.

Here, you can choose the Devices that you want to record and mute other audio tracks while recording, and then click the red button to start recording after a 3-second countdown.

Once finished, click the red button again to stop recording. Your voice will be saved to Media automatically, and you will get a copy and can save it to your computer (mav format).

Finally, you can edit your voiceover like music.