I have seen variations for this question, but most are several years old or apply to an image upload, so my apologies if this question has already been addressed.
We are using the Viart shopping cart program on our website, and there is an option to switch the editor over to CKEditor, which I have installed and activated.
However, when I am editing content, and I click on the "Link" icon, the popup window is missing both the "Browse Server" button and the "Upload" tab.
I don't know is I have neglicted to configure something in CKEditor, or if I am missing an addon, or if the problem is a conflict with the Viart program.
Any suggestions?

By default CKEditor does not
By default CKEditor does not include a file browser or uploader. You can, however, create a custom file browser or use an existing one, like CKFinder.
Documentation Manager, CKSource
See CKEditor 5 docs, CKEditor 4 docs, CKEditor 3 docs, CKFinder 3 docs, CKFinder 2 docs for help.
Visit the new CKEditor SDK for samples showcasing editor features to try out and download!