At each step, you should select the smallest weight edge available. To select an edge, click on its weightthe edge will turn blue. If the chosen edge violates the requirements of the cheapest-link algorithm (do not close a circuit prematurely and do not create a vertex of degree 3) the edge will turn red and an appropriate message will appear.
The cheapest-link solution will be obtained when the blue circuit is completed. A message will show the total weight of the circuit.