Will a Vivitar 75-205mm 1:3.8 MC Lens fit my Canon Rebel t7i or do I need some type of connector?
The Vivitar 75-205mm 1:3.8 MC Lens is an older film era, manual focus lens, and is not a direct fit for your Canon T7i.
You could use that lens if you have the correct adapter. That lens was made in many different camera mounts. You will need to identify which camera mount it has so you can buy the correct adapter.
Because it is a manual focus, manual aperture lens, you will probably find it difficult to use, even with the correct adapter.
The image quality from this lens will not be as good as what we have come to expect from modern lenses. It will be further degraded if the adapter uses an additional optical element as needed with some mounts.