There are two ways you can go about it depending what you want to do.
You can create a new assembly with the table as the fixed base part. Then you "insert component" and pick the part you want to put in the table assembly. Then locate your component with your "mates" commands. Typically it will be a face to face to put the part on the table, then you will use "distance" mates from the edges of your table.
The other way, which you have to use if your CNC package doesn't work in assembly mode, is to open your table file. Then you "insert part" and run through the mates command as you would in assembly mode.