HI I want to make a small table for the patio and will put tiles on top. what is the best way to preserve the wood on all sides before I tile it.
You may consider not using plywood at all. Once you frame the table, user cement backer board with a decoupling layer since those are the preferred substrates for tile.
Then you will have much fewer concerns about moisture, because the tile will be properly bonded, and provide its own waterproofing layer over the wood framing.