Okay, I'm really confused about what to do. I have the relic pieces assembled correctly. I read Jin's journal and looked at the comics to find the symbols. But I have no idea what to do next. I know that I'm supposed to open some prongs on the relic, but I have no idea what to do. Any help would be greatly appreciated. Thanks!

I would take a look at the walkthrough in order to help visualize what you are supposed to be doing and also to read the explanation of how it is solved:

The Shattered Medallion walkthrough

There are two pieces on the relic that circle each other. The outer circle has astrological signs, while the inner gold circle is used to complement this.

Use the comics to see the grouping of symbols necessary to complete the puzzle; the comics have some odd symbols in them.

You are trying to accomplish two things with this puzzle:
1. Move the inner circle with the arrow so that its specific segments (labeled with a rune) are aligned and pointing to stars mentioned in Jen's journal (see red writing to the right of the diagram).
2. Using the comics, know which astrological symbol corresponds to each pair of runes. Move the outer ring so that this symbol is placed near the pointed arrow of the inner circle.

If you have matched the symbols, runes, and stars correctly, you should hear a faint tick as spokes are removed from the middle of the puzzle.

Thanks for the help! I got it and finished the game!

Terrific!

Now we sit back and wait for Nancy Drew #31.