A string is a strand of fiber that's thinner than a cord or a rope. You can tie on a Halloween mask with a string, or weave a friendship bracelet with a bunch of colorful strings.
Strings are useful for tying up packages and cinching the waist of your sweatpants. You can also have a figurative string, a series or sequence: "Our team had a string of wins." As a verb, string means "attach together" or "thread onto a string." It can also mean "put strings on an instrument" — you might string your new ukulele, for example. And when you "string someone along," you mislead them on purpose over and over again.