1- Click one time on the canvas below to create a new vertex
2- Click one time inside the vertex to select it, After the selection Click on the other vertex to create an edge between them
3- To move the vertex click and hold the mouse on the vertex you want to move it, But you need to take on considerations that you       have not selected another vertex unless you are going to creat a new edge between them instead of moving the vertex you want       to move.
After creating your graph
4- Click in the button the start vertex and choose your start vertex