Q: I switched from a dell to a Mac. I put all my videos from dropbox onto my passport. Is there a way to use my passport that I used with my dell now using with a Mac without losing all of my data?

I don't know what a Passport is.   But I can tell you this, making backups from one source to another is quite possible.   Knowing how to network the machines is key.   Mac OS X: Sharing your files with non-Apple computers - Apple Support

The Mac can Read drives in many formats. Just plug the drive in and it should be recognized and mounted. Windows New Technology File System (ntfs) drives can be Read, but not written, without add-on software. Exfat drives can be Read and Written.

In contrast, Windows can read Windows drives. It does not believe there are any other Operating Systems.

It is likely formatted NTFS. To not lose anything and be able to write to the disk you have two choices:

- copy everything to your Mac and then format the drive is Mac OS Extended  (journaled) format and then move the files back to the external drive

- Purchases an app which allows a Mac to write to NTFS like:

http://www.paragon-software.com/home/ntfs-mac/