Slices are the way to store strings. At the end of the day, strings are just a bunch of bytes that are interpreted in an ASCII format. You'll have to interpret strings as such when working with them in the smart contract.

https://ton.org/docs/develop/func/literals_identifiers#string-literals

You can define strings with quotation marks like in other languages, but they are stored in such a way that they become a slice of bytes.

You can also store longer strings by creating a linked list of cells, see example here - SnakeCell