There are two ways to record walking or running once you click Record in the Biostrap app.
The first way:
Record > Gym Workout > Start
The "Workout" button will auto-detect cardio activities, and will detect other pre-trained activities you're doing.
The second way:
Record > Walking/Running > Start
The "Walking/Running" functionality will only record this activity, and has the additional option to map your route with GPS.