Pull up all the weeds from the area you wish to use tiles as a weed barrier.
Smooth the soil surface with a garden rake or hoe to settle any soil that was disturbed when you pulled weeds.
Place the tiles directly on the soil in any pattern that you desire. Place them as close together as possible for maximum effectiveness.
Tamp the tiles down lightly so fix them into position. You don't need any special tools -- tapping them with your hand or foot is sufficient.
Fill in the gaps around the tiles with small stones or crushed rock to prevent weeds from growing between the tiles. Ideally, the gaps should be minimal, but the crushed rock is extra security against stones.