Tertiary structure

This is the whole three-dimensional structure of a protein; it is generally a combination of several different secondary structures on each part of the molecule.
As an example, we can see lysozyme, which has a tertiary structure composed of:

several alpha helices,
one beta sheet, formed by 3 beta strands,
zones without a regular secondary structure

Use

These are simplified “cartoon” renderings; the closest to the real shape of the molecule is the style.
As you can see, this is a globular protein.