date

Use:

man date

or if you have a tldr client (like tealdeer):

tdlr date

Note: tldr is very sparse in detail. man has much more information.

Generate a Unix Timestamp

# Unix Timestamp
date +%s

# Long Readable Timestamp
date +%Y%m%d%H%M%S%N

Open a file with today's date:

# Your editor + the date expression + the rest of the file name + file extension 
hx $(date '+%Y-%m-%d')_<file_name>.md