For Algorithm learning, which things I should know ?

We should learn first for beginners:

• Reading in data from standard input (the console), or from a file. You must learn how to do this, since that's how interaction with the program is done.
• Basic arithmetic operations with integer numbers as well as real numbers.
• Basic operations with strings, like extracting a substring or reversing the string entirely.
• Arrays, iterating over an array, updating elements in an array
• .As you get more experience, you can learn about more advanced data structures. Vector, priority queue, map, and set are some of them. 

Resource Link: https://www.quora.com/For-an-ACM-ICPC-beginner-how-should-I-start