It needs to be replaced. Hire someone, that knows how to hang doors and do the frame and trim, and let them do it for you. It isnt something someone who doesnt know anything about it, to try doing on their own.

I agree with cat_ky that this is not something you will be able to fix given your admitted lack of knowledge. However, any halfway decent handy man should be able to remove those badly placed nails, and fix that piece back in place with glue, clamps, and possibly a couple of nails. It shouldn't take more than half an hour to do the repair, and you can paint it yourself once it's back together.

Buy this book: Reader's Digest Complete Do It Yourself Manual https://www.amazon.com/dp/0895770105/ref=cm_sw_r_cp_api_i_IiUlDbFQ5CMA7 (Definitely get the 1970s version, not an updated version.) It has so so so much useful info about how to do these types of household repairs and is very accessible for the total newbie. That is, the book explains all the materials, tools, and techniques you’ll need extremely thoroughly. Just make sure you do a quick internet search to cross-check safety stuff for any projects you’re planning because occasionally the book’s advice is something along the lines of “spray the entire area with asbestos, then enjoy a lead cigarette to celebrate a job well done.”

Pull the nail out from the back-side and put the piece back in place and re-nail. Use Bondo filler and touch up the crack, sand and paint and you will not notice anything, like it was never broken.

If you not handy enough to do this call a handyman and this can be fixed and touched up in 15 min.

Leave it like that maybe it will trend out

"Leave it like that maybe it will trend out"

Huh?