seniors please help. one of my forum shows catch writable warning below menu

[yourdailysaver]

please see attached file

[Illori]

can you set that folder to be writable? How do I chmod? / what is chmod?

[yourdailysaver]

but sir which folder ? and this message was not showing up before it started showing up today suddenly

[Illori]

cache, and i am not a sir.