Working with critique partners and beta readers is an important part of the editing process. These are people who are looking at your manuscripts when you have become too close to them and help you identify the weak areas. There are differences between critique partners and beta readers, each having a different focus and coming in a different stages of editing.
Your critique partners tend to be involved during the early stages of editing, looking at a story's development. As such, their purpose it to help you identify weak areas of your manuscript, where the writing itself needs to develop or you need to look more into the nitty-gritty of your subject matter.
A beta reader, on the other hand, looks at the full manuscript and is there to provide you with those reader reactions. You can even employ a special breed of beta reader known as a sensitivity reader, who is one who focuses on the way in which you handled the subject matter.
Understanding what these two different types of readers do is one thing. Finding them is something entirely different.