It seems that you are having difficulty getting the correct input and output dimensions for your state-space system model. In the case of a linear state-space system model, u is the input vector, y is the output vector, while x is the state vector. The block has one input and output port, corresponding respectively to u and y vectors. The dimensions of which depend on the dimensions of the A, B, C, and D matrices.
Input signal depends on the number of columns in B and D matrices, in your case it is 1 column. Further, Output signal depends on number of rows in C and D matrices, in your case it is 1 row.
I noticed that in the Simulink model you have shared, you have not included an input source for the vector u. This can be done using an Inport Block as shown in the image I’ve attached.
For the output signal, you can use an Outport Block, or a Scope Block as you have done. If you need to, you can display more than one signal using the scope block by changing the number of input ports.
Further, answering the question you listed in the title, you can use the ss Function to create a states-space model object.
