If you leave a comment on this question I will be happy to help you. There's too much to tell you at once, so I can guide you through it as you ask me questions.
How to diagram: My Five Steps
This section is not meant to teach diagramming. For that, see Workbook of Sentence Diagramming and Guide to Grammar and Writing. This section simply gives a "stripped down" 5-step method to break diagramming into bite-sized chunks. If you follow these steps in order, it will make diagramming easier.
Mark up the sentence.
In advanced sentences, mark the break between clauses.
In the basic level, put parentheses around prepositional phrases. Why? I have found that prep. Phrases cause more trouble than anything else. They get in there and disguise themselves as other things! So if you safely lock them away in parentheses until you're ready for them (Step 5), they can't fool you and cause trouble.
Find the verb and place it onto your diagram to the right of the vertical line. (See example.)
Find the subject and place it onto your diagram to the left of the vertical line. (See example.)
Why do I find the verb first and then the subject? There are usually more nouns than verbs in sentence, so it may be hard to know which noun is the subject. Once you know the verb, then ask yourself which noun is performing the action. That is your subject.
What kind of verb is it (transitive, linking, or intransitive)? Mark the verb type and direct object or complement (predicate noun or predicate adjective).
Place everything else onto your diagram. In basic sentences, "everything else" usually consists of modifiers (including prepositional phrases). Most modifiers go onto diagonal lines below the word they modify. (See example.)