There's no "n" symbol. "N" in this case stands for the total number of orbs that were shaking after you spoke with Tara.
Here's what should happen:
- Take the first symbol that Tara gave you, and locate it on the journal diagram. [The spider diagram]
- Now count clockwise however many spaces according to the number of shaking orbs.
- You've landed on a new symbol - that is one of the symbols to be entered onto the box.
- Repeat this process for the other two symbols given by Tara.
- Once all 3 new symbols are entered onto the box (in any order) you should be able to progress.
If you can't remember how many shaking orbs there were, then you'll need to go back to an earlier saved game and replay through the whole section with Tara. It's a randomly generated puzzle, so we can't give you the answer here.