I have a Half-elf Ranger. Having trouble using his speical abilities. Does it matter what type of armour he is wearing? Are they cast in the same manner as Mage and Priest spells?

You must not wear Armor heavier than studded leather to use the special abilities. Casting is possible with heavier armor, though.

Armour has nothing to do with a ranger's special abilities. You do not cast them in the same way as you do priest/mage spells. You cast them by clicking the star button in the bottom right-hand corner of the screen and then selecting the appropriate target.

Stealth: Cannot be used while wearing any armor greater than hide or studded leather (or a certain suit of chain mail).
Spells: Rangers are supposed to get access to the first 3 levels of Druid spells, as soon as they reach Level 8. Even though Rangers CAN hit Level 8 with ToSC installed, their spells are NOT implemented--you'll have to wait until BG2. Once they have their spells, though, armor is no impediment to casting, just as with any Priest.
Charm Animal and Minsc's Berserk: Use the Special Abilities button, just like Arledrian said.

Are you sure? I could have sworn I saw Minsc casting cure light wounds and stuff like that.

In the special abilities I noticed the my ranger has Larloch's Minor Drain and Charm animal. I know how to use charm animal. My ranger wears ankeg armour. How do I use the Larloch's Minor Drain.

Not in any of my games.....maybe it's a patch or version issue or something. Let's have a vote and see how many people can cast Ranger spells in ToSC, and how many can't.