Deleted all my pictures from camera roll but when i check my iPhone Storage, My photos usage is still the same

Just like in Windows, pressing the Delete key just moves your photos to the wastebasket, where they remain available in case your deletion was a mistake. In Photos on your iPhone, you should see a link called, "Recently Deleted", with the number of photos held in that folder. Photos go into purgatory there for thirty days, after which they are truly deleted. You can go into "Recently Deleted" and delete your photos at any time to free up your space.