OBS doesn't really do editing, it's designed for live streaming/events (hence Open Broadcaster Software (OBS)) but also handles 'VOD' (video on-demand) recording. You can do cuts on the fly as you record by configuring different scenes and using hotkeys but there's no timeline feature or post-editing features.

Camtasia is basically a NLE (Non-linear (video) editor) which has a screen recorder/A/V external capture function bundled though and can be used for splicing audio/video, adding basic effects/transitions and titles etc.

I suggested OBS if using OpenShot (which is also a NLE) as it's good for capturing screen/external video (capture card/webcam etc.)/audio content which then can be post-edited using OpenShot.