I see nothing in the manual about jumping up OR down, I thought it would highlight a mouse click, but when I go to where the arrows are pointing me to go, I'm just at the top of the wall and can't get down. ? Anyone?

If your in the right place, you will get a prompt to jump down. (See attached Pic)
Compare your mini map with the one in the Pic
The quest markers show you were to go, but not how to get there like witcher 3.
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Many thanks! I somehow missed that spot...really movement on a PC sucks, the mouse is way too sensitive no matter what settings I use.

I don't get you'd know how to fire the freaking ballista too? :) I'm standing right at it in the proper direction to fire but no icons appear.

Have you killed everyone in the area?
I think from memory, you can only use it when the area is clear.

OK I found the problem, there were a couple of guys just standing way back out of sight and not attacking. But now every time I cock the thing, more guys attack. I never get a "fire weapon" thing. ?

OK, yeah I just had to tough it out a few more rounds and click on the aim/fire stuff quicker, didn't realize at first that it mattered how quickly I did it. Yeah this is definitely not a game for a PC. Wish I'd realized that sooner! I didn't pay much for it so didn't lose much money, but not sure how much more I can get out of this game. Anyway appreciate it!

I think it's worth sticking it out.
That Ballista and a QTE fight in Act 2 are the worst.
The QTE's for fist fighting are always just W A S or D, so you just go by the position on the screen.