Sentence variety is of the utmost importance in writing. While, yes, the the basic sentence gets at the heart of the matter in terms of identifying who is doing what, we need to offer our readers more so that they want to read on to discover more information; the more color (variety) you add to your writing, the more engaged your readers will be...and that, my friends, is the ultimate goal: to hold your reader's attention.
Below you will find several button links (Khan Academy) that offer a wealth of information regarding video tutorials and further practice to enhance your writing even more so.