They can also be made of something, which can be positive or negative. On weapons, they affect "to-hit" and "to-damage", and on anything else they contribute to armour class. Avoid anything made of leather, wood, brass or bronze, these all have at least some negative attributes. Glass is neutral, it neither helps nor hinders. Weapon or armour etc. made of anything else is of benefit and the general rule is that the more valuable the material, the greater is the benefit. There are, however, exceptions. In particular, Ebony and Steel are above Amber and below Quartz. Best of all, for either weapons or armour, is Obsidian. By the way, something described simply as "Leather Armour" is not enchanted in any way, but avoid "Leather Leather Armour" like the plague.

They can also be enchanted to cast spells, like your Box of Immobilisation. The problem with these is that if you use them to cast their spell, they vanish when the last spell is used. There is a spell of Recharge Item, but sometimes this does not work and the Item blows up. I very seldom use these. The one exception is items of Implosion. Implosion is the only spell which will do significant damage to a monster you will meet at the end of the game, called a Terminator. These can eradicate members of your party in one attack, and need to be disposed of as fast as possible. If you find items "of Implosion", keep them for your non-sorceror/archer characters in the endgame.

Immobilize is like Paralyse. Its problem is the same as with most of the low-level spells - it only works reliably on monsters so weak you don't have a problem with them anyway. Sleep and Pain ditto. Suppress Poison or Disease are useful until you can get the corresponding more powerful spells which cure the condition. The Suppress spells don't remove the condition or cure the initial damage done, but they do prevent the repeat damage taking place so you can get the party to a Temple to heal. If any stat drops to zero in this game (including Luck!) your character dies. Be careful!

The Detect Magic spell is only important if you're using items which cast spells; it tells you how many spells you have left.

Yes indeed, monsters do cast spells, which usually manifest themselves as some sort of elemental damage, but in specific cases can send your characters to sleep, paralyze them, turn them to stone, and so on.

Miscellanea
The golden card grants you entrance to the Pyramids, and the reason you can't get is is quite simply that you're not strong enough yet to break the glass.

The "real genuine ring" can be important. It is the only unenchanted ring in the whole game, and it takes enchantment very nicely indeed. Use the "Enchant Item" spell on it before you sell it; a Noxious Diamond Ring (say) goes for a lot of cash! And of course, if it's a really good one, one of your characters can wear it.