You have a new rose bush. You might have carted it home from the nursery, or a box from your mail-order source may have arrived on your doorstep. That depends on whether the new rose is bare-root or potted, and whether you plan to plant the bush in the ground or in a container. A big hole. Take a look at your rose.
Most people dig a hole big enough to squeeze the roots in.
But your rose is still a baby. Imagine the eventual size of the rose bush, and you get some idea of how much room the roots are going to need. If you have done a good job preparing the bed, the rose roots will be happy growing out into the surrounding soil. Put the soil in a wheelbarrow. Fill the bottom of the hole with the new soil mix up to just below where the roots will sit.