Grammar is often referred to as the set of rules of a language, but it is more appropriate to consider it a resource for expressing ideas. It gives you a choice of how to write. These choices can affect the content of your writing, the organisation of it, and your relationship with the reader. Shorter sentences help you avoid grammatical mistakes and make it easier for the reader to follow the line of argument. If in doubt, split long sentences up into two or three. This is especially important if you find writing very challenging or if English is not your first language.
There are many online resources to help you develop your use of language. Here are some of our favourites.