Diagramming sentences is a way to visualize how the different parts of a sentence fit together. The subject of a clause goes in one slot, the verb in another, and so on. Words that modify another word are attached to the word they modify.
On this website, links to grammar and punctuation rules are available. Additionally, the site discusses in depth the steps of the writing process and the qualities of academic writing.
A thesis statement focuses your ideas into one or two sentences. It should present the topic of your paper and also make a comment about your position in relation to the topic. Your thesis statement should tell your reader what the paper is about and also help guide your writing and keep your argument focused.