The word "elohim" is generally recognized as a plural since it uses the Hebrew plural ending "-im" and, in the context of referring to false gods, is clearly used as a plural. However, Elohim who created the world takes a singular verb. So the grammar here is showing something that is both plural in a way and singular in a way. Some use this (reasonably so, I'd say) as Scriptural support for God as Trinity.
When we think or speak of specific works of God in terms one of the Divine Persons, that is a concession to our human limitation. It is easier for us to think about the Persons by attributing different roles to them, but, as Michael said, the works are done by the all the Persons of the Trinity.
I think this is one of the reasons that people cannot validly baptize in the name of the Creator, the Redeemer and the Comforter (as some have foolishly tried to do in order to avoid "gendered language"). Speaking that way is an inherently flawed understanding of the Trinity.