Green wood refers to fresh wood that has recently been cut in a mill and has not been treated or allowed to dry. This wood is springy and can be useful for a variety of construction purposes, but it will tend to dry out, especially in a dry climate. As the moisture is released from the wood, it can cause different types of warping and damage, especially if the wood has been cut into straight beams or boards.
Fastening the Wood
One of the oldest methods to prevent wood from splitting or warping while drying is to apply force along the length of the green board to keep it in position as it dries, using clamps or blocks. S-clamps or similar types of wood clamp can keep the wood affixed to your construction project while it dries, but be generous in the number of clamps that you use, and apply wood glue to the connection surfaces to encourage the wood to stay where it is, especially along the joints. Similarly, you could screw blocks in or use them as weights on top of the board.
Fastening boards or timber structures in this manner is not always effective and depends on a wide number of environmental factors, including the climate and the type of wood. Some types of wood lose moisture so fast that they almost always will warp, even with clamps. If you can exchange green wood for dry wood or wait until your green wood dries before using it, then do so since you probably will not be able to completely eliminate the possibility that the wood will crack, split or turn.
Treating the Wood
Chemical treatments can encourage the wood to dry without warping or splitting, trap moisture inside the wood or replace the moisture with other chemicals. Polythene glycol is used with smaller pieces of wood to displace the water and replace it with other chemicals that do not change the wood's cell structure when it dries. This chemical requires immersing the wood for weeks at a time and is mostly used at lumber mills, so it probably would be more practical for you to use a commercial wood stabiliser such as Pentacryl, which you can paint on the wood.
You also can try sealing the ends of a wooden timber with wax, which prevents moisture from escaping by blocking the ends of the board, where water evaporates most easily. This is intended to slow down the drying of the wood so that splitting or warping effects are minimised. It can be effective for simple construction projects, especially when used with clamps or blocks.