Let us start a thread to describe some commonly used Linux commands to manage the server. Probably this will help to the newbie who have less knowledge.
 To check the running processes:
Description: This command will display the current running processes on the server. This will help to monitor the current running processes. For more options of this command go through the manual of this command.
 To list the files and folders:
Description: This is command will list the files and folders which are in current directory. For more options of this command go through the manual of this command.
 To check running process by particular user:
Description: By adding some parameters to this command you can grep the processes owned by particular user:
ps auxf | grep username