OP:
What games do you play?
If you're new to the genre, it's best to start with titles closest to your favourite type of games.
If you're into massive multiplayer, DAI will be almost painless transition. If you're more into action-oriented experience and world reactivity, TW3 would probably be better choice. If you're looking for more organic combat experience, you should start with Dark Souls. If you're more into strategy - try Divinity: Original Sin instead. If you like customizing everything around you instead of playing game, wait for Fallout 4... or play the Sims.
Most ritfs will spawn two waves of hostiles, after second wave is dealt with, you can close the rift. Disrupting it during the fight will only stun hostiles for a short time. It's useful if you are overwhelmed or wait for ability cooldown, but sometimes it's not worth the effort, especially when you're taking most of the blows. When second weave is about to appear (they are not visible but you can spot them - look for circles), try using dispel/disruption (i don't remember the skill name, but it's a mage ability, spirit school iirc) - it should insta-kill some of the more annoying ones.
Play with skills, reset them and test drive, see how they work, what they do, how they work with others in your party. After some testing you should find your favourite playstyle. Possibilities are not endless, unfortunately, but for someone new to the genre it should be enough.
Also... grinding, as in killing massive numbers of hostiles to acquire items and sell them to vendors for gold, is the core concept of this game - but it's uncommon in the RPG genre. Fortunately there is crafting. The only grinding you need to do here is related to resources (leather, ore) and schematics (interesting ones are random drop from containers/dragons).
Grinding usually is time-consuming, that's why it's perfect for online games which require subscription, in free to play model you can invest money instead of time, its inclusion in single player game is quite baffling.