This is a very common question. Using literary critics is a great way to demonstrate any extra reading you have done and to show that you can engage with complex theories. When using a quote from a critic you should always engage with the idea they are putting forward by explaining how it is relevant to the argument you are making. This could be by saying how it supports your own idea or by saying how and why you disagree with their point. The most important thing to do is make sure that your argument is always the focus and that you are not letting the critic speak for you, this is a common mistake.