If you are not familiar with using shell (SSH) you will find the commands below a good start. They are amongst the most used ones by all the administrators worldwide.

top - this command shows information about the running processes on your server, uptime, cpu usage and memory usage. You will see the most resource-consuming processes at the top of the table;

ls - this command will show you the content of a directory;

ps -auxf - this command will show you the currently running processes on your server;

who - this command will show you the users currently logged via SSH on your server;

pwd - shows the directory you are currently in;

rm sample_file.txt - this command will delete the sample_file.txt file;

rm -rf sample_folder - this command will delete the sample_folder directory and all the content in it;

tail sample.file - this command will show you the last lines of a file. It is very useful when you read logs;

tail -n100 sample.file - this command will show the last 100 lines of the sample.file file;

mkdir test_dir - this command will create a new directory named test_dir;