Odoo does not offer a special functionality for table booking management. Anyway, there is a workaround for you to know if a table is blocked or not. 

If you want to book a table, you might first ensure to thick the "Is a bar/restaurant" and "Floors & Tables" checkboxes. 

Once your tables created in the PoS, you can define the number of seats. Now, here are the steps to book a table : 

1. Enter the table, you arrive on the order page. From there, enter the "Guest" button and add the maximum number of guests. You will be able to change that number later if needed. 
2. In the floors & tables view, you can now see that the table you booked for your client is in a darker colour than the ones where no guests are set. 
3. Now, if another client calls, you know that this table is not free.