Starting from v1.7 you can create simple & beautiful tables!
Create a new table
Simply drag the Table from the Insert list in the right sidebar
On iOS you need to tap first to the + sign on bottom left, and then pick Table from the horizontal list.
On Web similar to the Mac app, you can insert a table from the right sidebar.
Slash command (on every platform)
You can always use the '/' slash command to add a new table quickly, just type /table or the size of the needed table (up to 9), e.g. '/4x4'.