In the example shown in the picture below I would like to split the light blue polyline into two polylines on a specific node (circled with number 1) with QGIS (version 2.12.3-Lyon).
Given that the layer is already editable, and given that I have set the snapping options at 1 map unit tolerance and snap it to vertex, which tool should I use, number 2 or number 3? (I get the names in Spanish and the picture seems easier to identify for anyone).
How do I select the node (number one) once the splitting tool is active? So far, if I just click on the node, the entire polyline disappears.
I understand the explanations already given by @Knightshound and @Joseph in answers to question 'Polyline split at node in QGIS' but need more detail into how to correctly proceed.