To throw something open (usually a door or window) is to open something fast and completely. In Spanish, I think it would be sort of like "abirir completamente y de golpe" or possible "de par en par." It usually implies a sense of urgency or suddenness. And, really, I think this particular phrase is almost always limited to doors or windows. For example, I don't think you would say you "threw open a drawer" or "threw open the lid to the box." But, others might disagree about that.