[Lava]

1/. How do you use the rings for finding the circles?

You need to have the ring on (you = your main character, which whom the ring is attuned). Only then the portals show up and if you take of this ring, the portals will deactivate. And yep, you have one of the circles right, you just need to find the other three, but they should be easier!

2/. Pretty, pretty please can you give me a very mild general hint about how to activate the shards.

Once you have all 4 strange shards, they will become one item and then you'll be able to activate them from the quick slot - just as if you were to use a wand to cast a spell.

3/. I spotted a post about a basalisk dungeon earlier in the thread. Can I have a hint about what and/or where this is?

You can find in on the same area as Mutamin's garden. There's an entrance in one of the rocks on the lower half of that map.

sewers

Enter the sewers by grate between the Mermaid and the Temple of Ilmater and then, once you're down, go left and you'll see an entrance to a small new area.