I find it simpler just to use PowerPoint (though Keynote or any other program you're familiar with should work as well). Set the slide size to match the proportions of the image you need to create (and each of these social media platforms has its own specs). If you need e.g. an 800 x 200 pixel image, set the slide size to 8 x 2 inches. Boom. Instant proportions. Create the image you want, filling the slide and then export to PNG/JPG/Whatever. That'll usually give you a higher rez image than needed, but FaceaGramSpace will usually downsample it for you. Or better, use Irfanview or some other capable proggie to do your own downsampling to final size.