Open your inventory ( I key), left click the book to learn the SpellShield skill. It is one of many books you will find that gives you a skill or increase the level of the same existing skill. Your skills and stats are increased as follows -

"Upon leveling you will be granted five attribute points, which you can use to increase your characters stats. Strength, Agility, Vitality and Intelligence can all be increased, but the choice is fully yours allowing you to increase the stats as you see fit. Also upon leveling you will be granted one skill point, or two skill points if it’s a fifth level (5,10,15,20,25…) These skill points can then be spent on any skill you wish, providing its available to you."

This is a good walkthru site. The left sidebar gives detail info on items, skills etc. the right sidebar gives a step by step on each area of gameplay.

This is a good tips site for basic info. . . =)

For basic buy / sell / identify / repair check the attached images on this post.

The attached image on this post shows back use of the self-repair skill but it describes how to use most skills.

This post will give basic info on how to make potions from herbs and mushrooms.

Edit: Think of the catacombs and dungeons as a leveling up experience and a way to find better weapons / armor / charms. If you clear them completely, you will gain a few extra levels and skill /stat levels which helps greatly with the game play.

I failed to mention above, in order to read a spell book (use it) you must have an intelligence level that high enough to learn the spell / skill. If not, clicking on the book will do nothing, with enough intelligence clicking on it will give a little text msg indicating you learned a spell from the book and the book will disappear from your inventory. . .=)