Watch each command run in a real-looking terminal, see what every part of it means, then try it yourself with practice tasks. From ls to kubectl.
The first three commands on any server: where am I, what's here, and how full is the disk.
Read and change permissions and ownership, set defaults with umask, and use sudo and ACLs.
chmodChange file permissionsBeginnerchownChange file owner and groupBeginnerchgrpChange a file's groupBeginnerumaskSet default permissions for new filesIntermediatesudoRun a command as root or another userIntermediatesetfaclGrant per-user and per-group access with ACLsAdvancedgetfaclShow a file's ACLIntermediate