-Piklopedia-
The 'X' button allows you to read Olimar's notes, which provide basic information about a creature, including a Latin translation of their name and a family.
After rescuing Louie from the Dream Den, the 'Y' button lets you view Louie's notes on a creature, which are mostly notes on how to cook or sell a creature.
The 'A' button allows you to zoom in and take a closer look at a creature.

When zoomed in...
The 'A' button allows you to throw Pik-Pik carrots to see the reactions of a creature.
The 'Z' button douses a creature with Ultra-Bitter Spray.
The 'C' stick allows you to view the creature from different angles.

-Treasure Hoard-
The 'X' button let's you see Olimar's view on an item.
When you complete a series of treasures, the 'Y' button shows you a sales pitch of your selected item.
The 'A' button zooms in on a treasure.

When zoomed in...
Use the 'C' stick to view it from different angles.