gpg

gpg -o <output-file> -c <file-to-encrypt>

the argument -o takes the path to the output file (the encrypted one) and the flag -c tells gpg that we want to encrypt, you will be prompted to enter a password

gpg -o <output-file> -d <file-to-decrypt>

the argument -o takes the path to the output file (the decrypted one) and the flag -d tells gpg that we want to decrypt

to encrypt a directory, we simply compress it into a file:

tar -cvf archive.tar <directory>

for faster compression but bigger file size:

tar --use-compress-program="pigz -k -9 " -cf archive.tar <directory-to-compress>

and then encrypt that file