To paint is to fully paint a base coat, layer highlight coats, apply washes as neccessary, and base the model.
To prime is to apply a primer to ease the sticking of paint to the model while also providing a color contrast.
To assemble is to cut and fuse the model based on the mold so it is available to prime and paint.
To purchase is to go to either a local store or main store and purchase the models that will be assembled, primed, and painted.