I think, i begin to realize it.

For the simplicity of it......to start off with, the basic meanings... There was a significant difference in price - meaning large/ big difference Significant also means large in terms of importance. Scientists made a significant discovery. Largely important! - does this make sense? It is important to drink a lot of water every day. Meaning necessary, it is need

You asked a good question Maksim. A very, very difficult question to answer. :-) Firstly, if you are a learner at a lower level then it's okay for now to think of these two words as synonyms...or at least to know that native speakers often use them to communicate more or less the same idea. Most native speakers never think about the difference. Both words are used to describe something that is special compared to other things. For example: "There are 365 days in the year. Christmas Day is a special day in the calendar. It is the most important/significant day." - for most native speakers who don't study language this means exactly the same thing. BUT there is actually a lot of discussion about the difference between the two words. And it can be quite important/significant in science and data analysis contexts. Pages and pages have been written about it...I don't think that there's space for me to write a simple answer here...in short 'significant' can have a specific meaning in those contexts Remember that English has no official organisation that regulates the language, so it is flexible.... which can be frustrating when learning the language but is good when you are using the language. Does that help?

I don't understand even more

Hello Maksim, “significant” means “large or important enough to have an effect or to be noticed”. “important“ means “having a great effect on people or things; of great value”. I hope this helps, Wolf Clayton English