Without buying and selling, there can be no entrepreneurship. However, buying and selling are by no means the most important aspects of entrepreneurship.
Entrepreneurs must surely buy and sell. The whole point of entrepreneurship is to make money. It is not possible to make money without selling a good or service. It is very unlikely that anyone could make much money without buying something, whether it be raw materials or labor or both. Thus, buying and selling are integral parts of entrepreneurship.
However, the real meaning of entrepreneurship has nothing to do with buying and selling. What sets entrepreneurs apart is their ability and willingness to take risks and to be innovative. Entrepreneurs are special because they can see opportunities where others cannot. They are willing to take risks in pursuit of those opportunities. They are able to put together various resources in new ways that lead to economic growth. This is what is truly special about entrepreneurs.
Thus, entrepreneurship does involve buying and selling, but those things are not what make entrepreneurship difficult and important.