YMMV but I used a free trial of Adobe Premiere Pro to learn the basic concepts for editing clips produced by my Nikon D850 DSLR. At work I had access to Premiere Elements and decided this was good enough for me, as a hobbyist, given that going with Pro would massively increase my existing monthly fee to Adobe. So I paid the one-off license fee for Elements.
I'm currently looking at BlackMagic's DaVinci Resolve, which has a quite well featured video and audio editing package for free. But 'all' the free version does is edit video clips. You have to pay for additional functionality. Premiere Elements, in contrast, has lots of useful things like creating/handling non-video assets such as text for titles and credits, loads of (sometimes cheesy) clip transitions, etc etc. Resolve may be okay if you hate Adobe.
You'll need something more sophisticated if you are targeting non-standard playback devices, or want to participate in collaborative workflows, or grade raw sensor clips (assuming you can get this data off your video device). As a real power user you might also want to look at ffmpeg, something I simply haven't had time to get my head round.
Again, YMMV.
[Edit] I consider myself an 'advanced' stills photographer, who is much happier using manual rather than auto settings. When I started with video, however, I quickly discovered how much I didn't know. For example, what is the relationship between the shutter speed of the camera and the frame rate of the video? This was helpfully ignored in the camera's manual, and took some googling to find out. Video autofocus is also pants, on the D850, for the type of wildlife and action photography I like (it always refocuses just as the bird lands). So I'm teaching myself to use manual focusing, just like they do in the movies. A video tripod head was also essential so I could pan, elevate and focus with only two hands rather than three.