When something snars, it gets tangled or twisted together.
Snars are usually bad because they make things messy and hard to fix.
Examples:
The wires snars together and it's hard to fix.
I don't like it when my hair snars.
She tries to untangle the snars in the necklace.
The shoelaces always snars at the worst times.
The vines in the garden snars and make it hard to walk.
The yarn snars into a big knot.