I am playing this since yesterday and I am still wondering what certain items do (e.g. the mushrooms) and what the specific stats are for weapons and armour ... ?

How can I see those things ?

I was trying everything, and was reading the manual, however couldn't get any information. It's really frustrating not to know what items do, especially if you buy a pricey sword in a store...
I mean, for swords what kind of damage they do etc

How do I see this in the game ?

When you click the magnifying glass and then on an item, you get the description of that item.
It tells what damage it does, for instance.

Mushrooms do two things to you when eaten, one useful and the other is a temporary side effect ;-)