If you click on Theme, you can use one of the defaults themes Google Slides for your design, but if you need a more professional style, at Slidesgo we have a wide variety of templates, even with formats such as A3 and A4 already defined.In the example, we have used a vertical A3 format (29.7 x 42 cm) From the drop-down, select Custom and set the size. A small tab will appear where we can configure the slide. To adapt it to the size you want your poster to be, click on File > Page setup.
Open a new presentation in Google Slides.
