date +FORMAT prints the current date in the format specified by the format string FORMAT.

The formatting symbols used in the example:

• %B: the locale's full month name, for example "March"
• %d: the day of the month, padded with a zero when it's a single digit, so the 1st of the month becomes "01", while the 21st of the month is simply "21"
• %Y: simply the year, for example "2019"
• -: this is not a special symbol, it is simply printed literally, so "-"

See man date for the complete list of supported formatting symbols.