Shelf Installation
 

I just bought refrigerator shelves but not sure how to install them. The glass appear to be smaller tham the frame. Please help.

Here are your parts.
Replacement parts for FRT18G44AWE models | AppliancePartsPros.com

Cannot say what is going on without being there.

Take a look at the parts you ordered.
Click on their picture and a new page will open with better views and a Q&A section which may help.
To get the dimensions for glass Item 47, each square is 1 inch.