The thread passes through the opening, and a motorized wheel pulls it out when you press the button. Have a container ready to catch the thread as it comes out, and let the spool run out without applying excessive force to the reel mechanism.
The device runs on two AA batteries, not included. The retrieved line must be collected and disposed of in an appropriate container; avoid leaving it unrolled in the workshop. The compatibility listed applies to monofilament lines only; it does not apply to braided lines.