Step One: Let's begin your understanding by reading the first two pages of this Grammar Girl article. Goal: By the time you finish reading, you should be able to see the difference between sentences written in Active voice versus ones written in Passive voice.
Step Two: Do this quick quiz now, just to see if you can identify the difference.
Step Three: Read this resource. It provides many examples of the same sentence written in the active voice and the passive voice. Goal: When you finish reading this resource, you should be able to create two versions of the same sentence, just like the writer of this site did. If you can't, go back and review step one.