Measure your table's dimensions so you know what size plexiglass you will need. Use a tape measure to gauge the length and width of the tabletop.
Purchase a sheet of plexiglass from a glass company, hardware store or home improvement store. Most can cut the sheet to the dimensions of your table and shape it as needed.
Lay the plexiglass sheet on top of the table, then add other objects such as dishes or candlesticks. plexiglass is clear, so you will see the table top, but the plexiglass will prevent the table from damage.