Goal: 
Examine an existing software bug report issue in the Drupal core project, or in the project for a contributed module, theme, or distribution. Either close the issue, move it to another project, ask for more information, or note that it has been verified as a valid issue. This is known in the Drupal community as "issue triage".
Detailed steps: 
  1. Set up prerequisites: Log in and be ready to set up an Online testing site from Common Prerequisites for Contributors. (If you have a Local development site set up, you can use that instead of an online testing site, but this writeup assumes you want to use an online testing site).
  2. Choose a project to triage issues in, either Drupal core or a contributed module, theme, or distribution that you are familiar with. Find the issue list for the project. Note: If you would like to triage Documentation issues rather than software issues, the procedure is a little different -- see the Triage Documentation issues task writeup.
  3. Filter the issue list to category "Bug report" and status "Active". Sort the list by number of comments in increasing order (by clicking on the "Replies" column header twice).
  4. Choose an issue with few or no comments (meaning it hasn't already been replied to or triaged). If there aren't any, choose a different project. Click on the issue title to open the issue page.
  5. Read the issue and any comments it has, to understand what the issue is about. If someone has already verified that it is a valid issue, or if one of the project maintainers has already responded (or if they created the issue), find another issue to triage.
  6. If the issue is actually asking for support instead of reporting a software bug, see the Handle or refer a support request task writeup.
  7. Follow the steps in Identify duplicate issues to see if this is a duplicate of another issue. If so, you will have closed the issue and you are done.
  8. Your goal is now to decide whether the issue is valid. So at this point, you'll need to set up an online testing site with the latest development version of the project the issue is in (Drupal core or a contributed module, theme, or distribution). Even if the issue is marked with an older Version, you should probably test against the latest version.
  9. Attempt to reproduce the problem described in the issue. This can result in several possible outcomes:
    • If you cannot figure out how to reproduce the problem from the information given in the report, change the issue Status to "Postponed (maintainer needs more info)", add the "Needs steps to reproduce" tag, and add a comment explaining what you did (including what software version(s) you used) and what information you need. (See Creating or updating an issue report for more details on how to update an issue.)
    • If the steps were detailed enough to follow but you didn't see the indicated buggy result, change the issue Status to "Postponed (maintainer needs more info)" and add a comment explaining what you did (including what software version(s) you used) and what happened (adding a screenshot can be helpful). Alternatively, if the issue was created a long time ago and you used a much newer version of the software to test, you can change the status to "Closed (outdated)" instead, again adding a comment explaining that the issue is no longer valid.
    • If you believe the bug is valid, but it is really due to a different module or theme, then change the Project of the issue to the other module/theme, with a comment explaining why you are making the change. (Any issue that requires a contributed module or theme to reproduce should be moved to that project so that the project maintainer can review the issue and determine the cause of the bug.)
    • If you have tried the steps and can confirm what the original reporter saw, add a comment to the issue saying that you have verified that it is a bug. Add more information if you think it would be useful, such as a screen shot of the configuration and the result, or a description of an additional step you did that caused the bug to appear. (Also see the instructions for how to document the steps to reproduce an issue.)
  10. Update additional information on the issue:
    • Change the Version to the version you used for testing.
    • Check the Priority, Tags, Category, and Component of the issue. See Fields and other parts of an issue for information on these fields.
  11. Don't forget to click Save if you have added a comment or updated any fields on the issue.