  As smartphones are widely adopted, mobile applications (apps) are emerging to
provide critical services such as food delivery and telemedicine. While bring
convenience to everyday life, this trend may create barriers for older adults
who tend to be less tech-savvy than young people. In-person or screen sharing
support is helpful but limited by the help-givers' availability. Video
tutorials can be useful but require users to switch contexts between watching
the tutorial and performing the corresponding actions in the app, which is
cumbersome to do on a mobile phone. Although interactive tutorials have been
shown to be promising, none was designed for older adults. Furthermore, the
trial-and-error approach has been shown to be beneficial for older adults, but
they often lack support to use the approach. Inspired by both interactive
tutorials and trial-and-error approach, we designed an app-independent mobile
service, \textit{Synapse}, for help-givers to create a multimodal interactive
tutorial on a smartphone and for help-receivers (e.g., older adults) to receive
interactive guidance with trial-and-error support when they work on the same
task. We conducted a user study with 18 older adults who were 60 and over. Our
quantitative and qualitative results show that Synapse provided better support
than the traditional video approach and enabled participants to feel more
confident and motivated. Lastly, we present further design considerations to
better support older adults with trial-and-error on smartphones.
