ls                       = Shows what a folder contains
ls -la                   = Also hidden files (i.e. those with a "." ahead)
cd                       = Change directory
cd ..                    = Back one step
cd /mapp                 = Change to an exact folder
cp /mapp/fil.txt /mapp2/fil2.txt = Copy a file 
cp -r /mapp/* /mapp2/    = Copy the folder and what it containing
mv /mapp/fil.txt /mapp2/ = Move a file, folder or just change the name 
rm fil.txt               = Remove a file
rm -r /mapp              = Remove a folder and what it containing

--help = Shows the syntaxes of a command (i.e. ls --help)