In English, your verb needs to agree with your subject.
A common mistake – especially in writing – is with subject and verb agreement. Sometimes the error is due to carelessness – you simply missed the mistake when you were checking your work. Sometimes it is tricky to remember all the different rules about subject-verb agreement.
By the time you’ve finished reading the rules about subject-verb agreement, you should be more familiar with the exceptions, and hopefully more aware of any subject-verb agreement mistakes you frequently make.
For the basics, try Purdue Owl here. For a more comprehensive look at subject-verb agreement, try the Grammar Monster here. Similar information but a different layout is here – just to check you’ve understood!
Do you struggle with there is and there are? BBC Learning English has a look at the difficulties here.
And if you’ve caught the subject-verb agreement bug, then go to Wikipedia for an in-depth look at English and other languages.
Need one final look at the rules? Of course you do! Go here for 20 rules of subject-verb agreement!