"CC" means that it is allowed to share (copy, redistribute) and to adapt (remix, transform) the licensed matter for any purpose, even commercially.

"BY" means that the licensee must give appropriate credit, provide a link to the license, and indicate if changes were made. He or she may do so in any reasonable manner, but not in any way that suggests the licensor endorses the licensee.

The complete license is available here: https://creativecommons.org/licenses/by/4.0/legalcode