Hi @mbeck007 Welcome to the Forum.
It is assumed that you are not using the Pro version of S3D.
Search, available top right of every Forum page, for Importing STL and it will reveal a lot of information.
These articles may be of interest:
https://discourse.shapr3d.com/t/supported-import-formats/4778
https://discourse.shapr3d.com/t/explanation-of-export-import-formats-supported-by-shapr3d/279
Happy S3Ding