Correct, if the seller didn't include the textures in an embedded OBJ/FBX file they will need to be manually placed in a material then applied to your object. Even if they are embedded they will not appear correctly for your render engine as they use legacy material formats. Usually the textures should be included in a texture folder or rar/zip package - if there is no textures provided then you will have to source your own.
This is why I provided you the above tutorials, this will give you a basic understanding of what textures go into what slots for your material (Diffuse/Reflection etc). Once you understand how each texture affects the material you can confidently create each material for your geometry object.
Also note that if the model you purchased did not come with any textures or is just grey in the preview, you will have to either check the details or contact the seller first to ensure the geometry is UV mapped and ready for texture stage. If not then you have a lot more learning to do.