Haha, well yes this is me officially getting into these games, and they're good so far. I played them as a kid but preferred games like Final Fantasy at the time.
So how do I know if an item is magical, cast detect magic? Then do I have to get it identified at a shop?

Yes.

Although with experience you'll get a pretty good idea of which items are magical or not, without having to cast Detect Magic.
One method is to equip items and see if THAC0 or AC improves. Some items are cursed, though.

Thanks and are you actually a cat

A safer method instead of equipping is to try to sell at the shops. If the offered price is high( as in 1000 or more) then the item is magical. You can then have the shop ID the item.