Curved wood is different from warped wood. Curved wood typically variates from side to side. Warped wood bends up or down. In production lumber mills, curves are dealt with by running the boards through a machine known as a straight-line rip. But if you buy your lumber rough-cut, the edges will curve. You will need to straighten the edges before you can use the lumber. Do it on a table saw.
Lay the board on a table saw parallel to the fence. Place the curved side facing left, away from the fence. If the wood is severely curved, it may only be touching the fence at both ends of the board, that's OK.
Slide the fence in the direction needed so that the blade will cut down the outside curved edge of the board. It's OK if it doesn't cut off the entire edge the full length of the wood. The goal is to just cut a flat spot on the outside edge.
Turn on the saw. Carefully feed the board into the blade, making sure that the board stays tight against the fence. Push the board all the way across the blade, cutting the outside curved edge off. Turn off the saw.
Flip the board over so that the fresh-cut edge is facing the fence. Slide the fence over so that you trim 1/4-inch off the outside edge. Turn the saw on and push the board through the saw. Turn off the saw.
Flip the board over. Reset the fence 1/4-inch closer to the blade and run the board through again. Reset and run the board through again or until one edge is perfectly straight.
If your wood is severely curved; typically more than 4- to 6-inches side to side, don't attempt to straighten it on a table saw. Reject it. Make the lumber yard replace it.
Be very careful and keep two hands on the board at all times. Wood can kick back. Straightening wood on a table saw takes a cool head. If you have any apprehension about doing it, make sure you have an experienced woodworker on hand to help you.