Что это?

Эластичная повязка, часто используемая в физиотерапии.

Где его найти?

Physical and Occupational Therapists might have Therabands in their office or sensory gym. Classroom Teachers might also have extras around the room.

Как мне его использовать?

You can use a Theraband in activities that require some resistance. Another common use is to tie it to the bottom of a chair or desk for students to put their feet against and push/bounce as necessary. This gives sensory input and lets their feet stay busy.