Linear codes have diverse applications in secret sharing schemes, secure two-party computation, association schemes, strongly regular graphs, authentication codes and communication. There are a large number of linear codes with few weights in the literature, but a little of them are minimal. In this paper, we are using for the first time weakly regular plateaued balanced functions over the finite fields of odd characteristic in the second generic construction method of linear codes. The main results of this paper are stated below. We first construct several three-weight and four-weight linear codes with flexible parameters from weakly regular plateaued balanced functions. It is worth noting that the (almost) optimal codes may be obtained from these functions. We next observe that all codes obtained in this paper are minimal, thereby they can be directly employed to construct secret sharing schemes with high democracy. Finally, the democratic secret sharing schemes are obtained from the dual codes of our minimal codes.