Dates in Tana keep everything connected to time in your graph. Just hit @ and write either today, tomorrow, or a special date.
This way, you connect all the data in the graph to that specific date, and you can find connections to it when you need them.
You can have dates in fields or mention dates in a line of text. In fields, it will look like this and appear on your Today-page:
The latter will look like this:
Remember - don't write 01/01/23 - use the @ so it connects to the items in your graph.
Generally, if you want to write searches for nodes and display the date as a column or sort by that date, you'll want to put the date into a field rather than mentioning it inline.