What should I use to create my poster?

You can use whatever software you would like as long as the poster can be converted to a PDF or JPG. There are some free online sources available that make posters really easy to create like Canva, Adobe Creative Cloud Express, and Pic Monkey. You can also create your logo on Canva or try some other options like Wix and BrandCrowd. If you are more familiar with Microsoft products, feel free to use Word or Publisher to create your poster.