If I go to a retirement home, what will I do all day?

As much as you can . Retirement homes, assisted living or adult homes all offer some assistance with activities of daily living: eating, dressing, toileting, bathing, medication... There are planned schedule of leisure activities daily, and one can choose whether or not one wishes to participate. Most importantly, there are many social activities, entertainment, religious services, movies, exercise classes, day trips.
Most retirement. facilities have an Activities department that plan daily, weekly, & monthly activities for the residents. As you consider moving into a retirement facility, make sure to check their activities calendar to see if they have offerings that appeal to you & also speak with the Activities department to see how open they are to helping you get/find activities that will be of interest to you.