In this instance the "couch" is a generalized term to reference anyone that may be leading a sedentary (not active) lifestyle to begin with. It's difficult to define what this means to different people because of the wide variety of individuals who use the app, so don't be discouraged! There are many variables to consider like age, weight, experience, and lifestyle (what you do for work). I, myself, walked exclusively for about a year before I attempted to dive into a 5k protocol. Even then, my body was greatly limited in the beginning in terms of stamina and mobility (and I'm still in my 20's).
Nowadays I prefer running for cardio but have to limit the number of days I do it because of the incredible load it can put on your knee joints. If your body isn't accustomed to this stress it's best to tone it down and work your way up to it. In terms of the motivation, you could use that first day as your first goal to reach and create steps to achieve it. Try not to compare where you are now to where others are in their journey, it's simply not fair to yourself.
IE: First day walk for the 30 minutes and see how you feel. Turn it up if you have the energy and wherewithal. Next day, start your walk and attempt a 30 second run. Gauge how you feel and perhaps attempt a second 30 second run, or even several 15 second runs. You'll know what's best for you based on how you feel and energy levels. The only rule of thumb is to seek progress day to day.
The intent of the app is to give you an idea of where to start and steps toward progression. The start point in the app isn't necessarily your start point and that's a-okay! Gives you something to work toward in the future :)