Your device's clock decides whether it's still yesterday's Hebrew day or already tomorrow's. Toggle sunset, see this week's parsha and the next holiday, then convert any other date both ways.
Reading your device’s clock…
The Hebrew (Jewish) date is not one fixed number for a calendar day the way the Gregorian date is. It changes at sunset rather than at midnight, so the same civil evening can belong to two different Hebrew dates depending on whether the sun has set yet. That is why this page reads the visitor's own clock rather than a server's, and offers a toggle for the case a device's clock cannot resolve on its own: whether sunset has already happened where the visitor is.
Once the calendar knows which Hebrew day it is, everything else follows: which portion of the Torah is read this coming Shabbat, whether a holiday falls today or is still ahead, and how to convert that date to and from the Gregorian calendar most of the world uses day to day.