Tables are regular blocks, so they sit between paragraphs and move with the note.
Inserting a table
On desktop, type / and choose Table, which inserts a table with a header row. On mobile, tap the table button on the toolbar above the keyboard.
Editing on desktop
Open the menu on any cell to insert rows above or below, insert columns left or right, delete a row, column or the whole table, merge and unmerge cells, and move rows or columns around. Column and row edges can be dragged to resize.
Editing on mobile
Tap the small grip on a row or column edge to open a menu with insert row above or below, insert column left or right, and delete row, column or table. Merging cells and moving rows or columns is desktop only for now, and a table built that way still displays fine on the phone.
When a table is the wrong tool
Tables are for short structured facts. If the cells keep growing into sentences, the content probably wants to be headings and paragraphs instead, and search will treat it better that way too.