The National Institute of Mental Health (NIMH) has many pages which provide basic, understandable information about various mental health issues.
Last month I linked to their general site. Here is a link to their page on anxiety. According to NIMH, approximately 40 million American adults ages 18 and older, or about 18.1 percent of people in this age group in a given year, have an anxiety disorder. That's a lot of people, so if you're reading this and you're dealing with anxiety, realize you are not alone and there is help for managing anxiety.
At the link above, you can learn aboutcauses of anxiety, signs and symptoms of anxiety, who is at risk for it, treatment options, and ways to live with anxiety so that it doesn't control your life.