When invoked without arguments, the date utility displays the current date and time. Otherwise, depending on the options specified, date will set the date and time or print it in a user-defined way.
# To display the current date using the default locale's format:
date +"%c"
# To display the current date in UTC and ISO 8601 format:
date -u +"%Y-%m-%dT%H:%M:%SZ"
# To display the current date as a Unix timestamp (seconds since the Unix epoch):
date +%s
# To display a specific date (represented as a Unix timestamp) using the default format:
date -d @1473305798
# To convert a specific date to the Unix timestamp format:
date -d "<2018-09-01 00:00>" +%s --utc
# To display the current date using the RFC-3339 format ('YYYY-MM-DD hh:mm:ss TZ'):
date --rfc-3339=s