When you disentangle something, you free it from a snarl or tangle. If you have long hair and pierced ears, you've probably had to disentangle an earring from a curl of hair.
Something that becomes tangled or twisted needs someone to disentangle it — you might disentangle your kitten from a length of yarn, or disentangle your jacket from a thorny bush when you're hiking through the woods. You can also disentangle someone figuratively, helping them get out of an uncomfortable or difficult situation. Tangle is at the heart of disentangle, from the fourteenth century word tagilen, "to involve in a difficult situation."