--- or :--- for left, ---: for right (numbers, usually), :---: for centre. Bold, italics, links, chips and dates work inside a cell as they do anywhere, and a cell can be empty.
The separator is the one place smart dashes could get in the way, and they stand down there: type | --- | --- | with them on and the hyphens stay hyphens, where before they became an em dash and the table came apart. A separator that was already turned to | — | — | somewhere else — in a message, say, before it was pasted — still reads as a table here, and a paste straightens it.
Moving about
Tab goes to the next cell and selects what is in it, so typing replaces it; ⇧Tab goes back. Tab from the last cell of the last row adds a row. Outside a table Tab keeps its other meanings — nesting a list item, picking from the slash menu.Starting one
/table in the slash menu writes a two-column table with a header, the first heading selected and ready to be typed over; /table 3x4 writes three columns and four rows, the header among them (/table 3 is three columns). A table pasted from a web page, a spreadsheet or a document arrives as a pipe table already, and so do cells separated by tabs — a selection copied out of a spreadsheet, or a table a page handed over as plain text.

