Linux / Unix : How to remove files and sub directories in the particular directory Recursively?

To remove files and directories recursively use r or R option with rm.

rm -r directory

which removes the directory, its sub-directory and its files.

For example:
animals
wild_animals
tiger.txt
lion.txt
pet_animals
cat.txt
dog.txt

$rm -r animals
deletes animals , wild_animals & pet_animals (sub directories) and its files.

With r option, you can use f option to force to delete. It won't prompt before removal. If you want prompt before remove, use i option with rm.