I purchased a template that included a Collection of Work pages, however, every time I try to add something like a video or change a photo, these changes are automatically also made to the other pages in the collection. How can I make it so this no longer happens and allows me to add different elements to one page without them applying to all the others?
Here is my site Read-Only: LINK
(how to share your site Read-Only link)
If you want to add a photo, video or any other content on one collection item but not the others, try using a Rich Text Field instead.
Here’s an explanation on how Collection pages work:
Here is how to use a rich text field in a Collection:
Hope this helps 
As Nelson says, rich text is your best tool here.
However if you have a limited range of layouts and want to vary them, e.g. this collection item page focuses on the video, that one on the podcast, the other one on a lightbox gallery… you can use this technique…