To anchor Trex to concrete, use concrete screws or anchors designed for outdoor use. Firstly, position the Trex board where you want it and mark the screw hole locations. Then, drill pilot holes for the screws or anchors, ensuring they are slightly smaller than the screw diameter. Next, place the Trex board back in position and insert the screws or anchors into the pilot holes. Use a drill or screwdriver to tighten them into the concrete until secure. It is crucial to follow the manufacturer's instructions and guidelines for the specific screws or anchors you are using. Proper anchoring ensures the stability and longevity of your Trex board on concrete surfaces.