While getting your home done, there are 3 professionals who can help you typically with design, product selection and execution: architect, interior designer, decorator.
Each of these 3 types of professionals help in different ways:
An architect can help you with extensive renovation, civil changes, reconstruction work and is registered to sign off on drawings for municipalities etc. Many architects take up interiors works and bring to the project, in addition to design, more technical understanding of materials, construction techniques and project management. Design means, furniture, lighting, colours, wall textures, curtains, and the entire package with 3D visualisation effects. The drawings that are sent for execution tend to reflect both design and technical details.
An interior designer is qualified to do the same as an architect with lesser technical knowledge on the construction technique and process with more emphasis on the design. The 3D visualisation, selection of finishes, actual furniture design is usually the expertise of the interior designer.
An interior decorator may not have any technical expertise but may be talented/trained to pick out décor items like art work or curtains or wall paints/wall papers. They may curate furniture, suggest looks. They may not provide drawings, costs, full interiors, civil works etc