Chairs and tables are added as symbols from the Furniture section of the Symbols Panel.
Open the Symbols Panel. By default it is on the left of your screen. Click Symbol Library at the bottom of the panel.
Select the Furniture category from the drop-down box at the top of the panel.
Click on the chair or table (don't click and drag), then move your mouse and click where you want to place it.
Move your mouse in a circle to set the rotation, then click. Hold Shift to lock the rotation to 45 degree steps.
To add more, copy and paste the symbol (Ctrl + C, Ctrl + V), or use a rectangular array to place rows of them.
Can't see the Symbols Panel? See Symbols Panel.