After being sentenced for a crime, you might feel that the sentence that you have been given is unfair. There are many reasons that the sentence might actually be the wrong one for whatever crime you did. This is because specific crimes are given different sentences based at least partially on the opinion of a judge and different judges might see the same crime differently.
In order to have this sentence reduced, you have to make an appeal and appear in an appellate court. Before this can even happen, you will need a written opening brief which explains in a professional manner why you want an appeal and what you hope to present at this appeal. Having an experienced professional prepare this brief is much better than doing it yourself.