I’m new to private trackers so I’m not entirely sure what a ratio is

You want a certain file (movie, music, software, anything).
There are many websites, which we call torrent trackers, that help you connect with other people that have this file. So these people will send you some parts of this file, 1 person called A will give you 1/3rd, another one called B 1/2, and let's say another one called C the rest, which is 1/6th. Taking a book analogy, for exemple if a book is 300 pages, person A will give you page 1 to 100 (1/3rd), person B pages 101 to 250, person C pages 251 to 300.
Any file, depending on the content, have a weight associated with it; the same way a bigger book weighs more than a light book. For exemple a movie can weigh 6 Gigabytes.
The website that helped you connect with other people and thus get the file, will save that information: A3R0PLANES got a file which is 6 Gb. But person A sent 1/3rd so 2 Gb, person B 3 Gb, person C 1 Gb.
Ratio is simply what you got from other people divided by what you sent to other people.
If person A downloaded a file that is 1 Gb, his ratio is 2 Gb (what he gave you) divided by 1 Gb, so his ratio is 2.

@A3R0PLANES
you download a torrent that's worth 1 GB. You leave it to seed in your client. You make upload, when others are downloading from you. So the ratio of the exact torrent will be 1:1(=1), in the moment you have uploaded 1 GB worth of data. This principle stays the same no matter the size- it could be a 100TB torrent, if you've only uploaded 50TB- your ratio is 0,5(50%). You'll need to upload 50TB more to get it up to a 100TB. Maybe look at it like its percentages in maths.
So that's it. I'm not sure how to break it down more easily. If you need more info, just ask me in a pm. Would be glad to help