Hello!
I unfortunately cannot answer multiple questions in one answer, but what I can tell you, is the difference between a complete sentence and a fragment taken from one. A complete sentence would be "When Catherine rode her bike to the store, she bought ice cream and cookies."
A fragment is taken from a complete sentence, and it looks like this.
"When Catherine rode her bike to the store."
Hope I helped!
Have a wonderful day! :)
-L