I am beginner just like you. My advice, go to problemset and click at "solved" button and you'll see the problems will be ordered according to number of people solved. Start from the top, if you find them difficult then you should go learn some math or solve them in a piece of paper instead. If you are bumping into runtime errors then you should learn a language properly.

a2oj.com you can find many problem catagorized, also there are some ladders which pretty awsome

Definitely go to USACO Training if you want to prepare for USACO. USACO's training site is based off USACO/IOI problems and has tutorials to teach you how to solve problems, so if you are preparing for those competitions, you should go there. Also, make an USACO account (separate from USACO Training account) so you can practice past USACO contests.

Also, CodeForces has a lot of problems in Problem Set and past contests have editorials so you can learn solutions to harder problems. CodeChef also has a lot of practice problems, some from past contests with editorials.

Finally, try to Google certain problems if you don't know solutions if you get stuck on USACO Training. Don't Google "how to solve usaco problem name," Google something more general that you're getting stuck with so you'll learn how to solve that type of problem instead of just learning the solution to that problem. Often, when I did this, I got tutorials from CodeForces or GeeksForGeeks that helped me for that problem and for problems I encountered later on.

Also you can visit here use chrome to translate it. It has many algorithms and nice implementation in C++.Hope it helps....