If by "witch" you mean the assassin in the tutorial, try setting the difficulty slider lower, that's what it is there for.

I can imagine the combat taking a bit to get used to if you're not experienced in this type of game. When in close combat, try holding block and make short quick attacks between the opponent's attacks. I'm sure someone here can explain the technique better than me.
Your hardware seems good enough, if you're having problems with stuttering (especially with many actors on screen), try playing around with the graphics settings.
Edit: Oh and by the way, good job on Abe, I could never get very far in those games.
Hi!
Thank You
I am at the last cavern,
A very large cavern withe several fires burning
Also a rat beig rosted
Going from here I find a "goblin witch"
kills me with lightning
I always die before I can stop him

They might mean one of the goblins. The ingredients might make it look like something you'd describe as a witch more than an assassin.
So, GAIO, please give us some more information about where you are and how you're having trouble and we're do what we can to help you through it. I'm sure you'll enjoy it once you get the hang of it.
Another method of sword fighting that I use is to run toward and away from my opponent at the right times. Stay back while they are attacking, then hit the attack button and then step forward so that you're close enough to hit them just as you swing. Then step back again. That way you're only in danger while you're doing damage. Maybe it's a little dirty but I consider it valid (non-cheating) since you could potentially use the same method in real life.
Hi!
I need lots of practice with timely movements!
I am at a very large cavern with several fires burning
Yes he is a "goblin witch" which kills at large distance with fire balls (lightning).. I have no chance of surviving.
I am going the wrong way but ...
Where is the wright way?
If you think I should find it please let it be
I am practicing acrobatics to discover how high can I jump to overcome barriers.
Hiding from this goblin witch doesn't get me any where and he moves fast ...

Don't get offended with my poor English but I am trying my best all the time.
Also
[Edit: Merged the two posts for you.]