The last important step is the post-production. This too is divided into several phases. If you mess around in post-production, all of the previous costs and efforts can be wasted.
Post-production usually begins with the editing of images and sound. All the material is viewed and then lined up piece by piece.
Then the special effects (CGI), the color grading, the sound design and soundtrack are made. The same rule applies here: every single element must be of high quality. If you mess at one point, it has a negative effect on the whole product.