Meaning of conditional statements in if[] then statement in makefile

What is the meaning of following conditional statements used inside "if":

@if [ ! -d "${OPENSSL_SOURCE_PATH}" ]; then \
fi

if [ -e "${OPENSSL_TAR_PATH}/${OPENSSL_TAR_FILENAME}" ]; then \
fi

Where can I find information about all such conditions like -d, -e, -f etc. ?