I am very new to codeforces and in the field of competitive programming. I just have given my 1st contest yesterday. I was able to solve 2 problems. from now on I will give every contest in codeforces. But I don't understand how will I practics as a beginner. what is the problem that I need to solve in order to get a good rank and to build confidence as a beginner.

some of the questions I have in my mind are:
1. what are the important questions, data structure, algorithm and maths concept should I do in order to able to solve div2 A B C problem?
2. what should be the strategy for best practices as a beginner?
3. how many questions should I do daily?
4. some times when I read an editorial I don't understand how this maths formula applied in this problem and form where this formula came from?
5.what are the thinks that I should focus in competitive programming?


I need your suggestions. pls, suggest something.
I need little guidance. if anyone is happy to guide me then pls message me.