There are many ways to get to a Structure database record. This illustration starts from a Protein record.
If there is an experimentally determined Structure for the protein available, a thumbnail of the structure appears on the right hand side of the record.
This example comes from a the MCM6 gene:
Clicking on the image, you will be presented with the Structure database records associated with this protein:
Choosing the structure for this protein returns the Structure Summary page:
Clicking on the View Structure link will download a file of the structure in .cn3 format. This can be viewed locally using the Cn3D program available from NCBI.