need a little guidance to download onto an external HD

I tried searching before asking but didn't find answers close enough I could figure out how to adapt--so hoping someone can help pls. I have RD and Syncler+ accounts. I'm going camping this summer and want to load some shows/movies onto an external hard drive so we can watch if there's bad weather and we are trapped inside (without wifi or internet so just using Syncler is not an option). what is the easiest/simplest way to do this? I am not super tech savy but can usually follow directions lol thanks so much for any help