Lock/unlock player

I have an older model I really like except it’s so small I can’t find often…wife was using iPod & iPhone for audiobooks - problem was everytime we’d try to transfer downloads from the library it was an ordeal.   So, I buy her a clip-sport, but the “lock” button was not obvious- just about took it back and then got on this forums page - glad I searched the lastest msgs cause early on it was all bitchn about no lock feature…it shoud be in the directions…