Pick a round
Codeforces runs rounds by division. Div. 4 is rated for people below 1400, Div. 3 below 1600, and Div. 2 and Educational rounds below 2100. If you’ve never competed, start with Div. 4 or Div. 3. The first problems are written for people at your level, so you’ll leave with at least one solve.
Register from the round’s page before it starts. Times show in your own timezone once you’re logged in, and Arise’s contest calendar lists the upcoming rounds.
Don’t wait until you feel ready. The first round is mostly about learning the interface and the clock, and the rating system below makes an early bad round cheap.
Know how the round is scored
Div. 3, Div. 4 and Educational rounds use ICPC-style scoring. Every solved problem counts the same, and ties break on penalty: the minutes from the start to each accepted solution, plus 10 minutes for each rejected attempt on a problem you solve later. After the round there’s a 12-hour hacking phase where anyone can submit tests against accepted solutions, then the final tests run.
Regular Div. 2 rounds score differently. Each problem’s points drop as the round goes on, and a rejected attempt costs 50 points once you solve the problem. During the round your code runs on pretests only. The full tests run when it ends, so a solution that passed pretests can still fail. People call that FST, for failed system tests.
Either way, fast early solves are worth the most. A clean A in the first ten minutes does more for your result than a heroic E nobody else solved.
Spend the two hours well
Read A, solve it, then read B. Problems are ordered roughly by difficulty, and early solves count most in both scoring systems, so reading all of them first mostly costs time.
Before you submit, run the samples and one case you made up, like the smallest input. A rejected attempt costs 10 minutes of penalty or 50 points, which is more than the minute it takes to test.
If you’ve been stuck on a problem for 20 minutes, look at the standings. They show how many people solved each problem. When C has three times as many solves as B, try C. Use the whole time: a solution accepted in the last minute still counts.
What happens to your rating
Ratings update a few hours after the round, once the final tests and any hacking phase finish. A new account shows 0, and Codeforces adds 500, 350, 250, 150, 100 and 50 points to your first six rating changes. Your displayed rating climbs quickly at first even if those rounds are average.
After those six rounds, the number starts meaning something. Compare it with where you were a month ago. Other people’s ratings say very little about your own practice.
Link your Codeforces handle on Arise so accepted solutions tick off on their own, then go back to the problems you didn’t solve. That’s the next guide.