File permissions

chmod
You can change file permissions with:

[r] = number for root permissions, [g] = number for group permissions and [u] = number for user permissions.

7 = 4+2+1 (read/write/execute) 6 = 4+2 (read/write) 5 = 4+1 (read/execute) 4 = 4 (read) 3 = 2+1 (write/execute) 2 = 2 (write) 1 = 1 (execute)

chown
You can change owner and group of file with:

You can change owner of folder and files inside recursively with:

gpasswd
You can add user to group with:

You can remove user from group with: