Ok kiddo, so you know how sometimes people study really hard and do a bunch of research to become experts on a certain topic? Well, in some countries like Russia, one way to show that you are really smart and knowledgeable about a topic is by getting something called a "candidate of sciences" degree.
Basically, this means that someone did a lot of studying and research on a specific topic, like science or history, and wrote a big paper called a thesis to show what they learned. Then they had to defend their thesis in front of a group of other smart people who asked them lots of questions to make sure they really knew their stuff.
If they did well and proved they were an expert on that topic, then they got the candidate of sciences degree, which is kind of like a medal to show that they are really smart and have a lot of knowledge about something. So it's kind of like winning a really big game or getting a gold star for being super smart!