Stardates Explained - 20181215.0000

You don't understand the startdates?

Take, for example, 20181215.0000

Let me stick some spaces in some helpful places:

2018 12 15 . 00 00

That better?

20181215 means 15th December 2018, and 0000 is in 24-hour clock format, IE 12:00 midnight

Stardates in the Star Trek universe work in an entirely different way. Wikipedia has a good explanation on how Stardates work.