I don`t manage to move a vertex. I read an answer on this question, but even though, I am not able to move it. And I am not able to prolong a line.
If you want to move a vertex you need to do start editing -> Select vertex tool -> select the vertex you want to move and move it:
Thanks to Matthias Kuhn who provided more details about the tool. In QGIS 3.x the behavior of the vertex tool is different from QGIS 2.x. In QGIS 3.x it is a click-click behavior, which means you need to click on the vertex that highlighted in red circle, then move the vertex (no need to keep holding the left mouse) and click again to release the vertex on the target location:
The advantage of this tool is that:
- User clicks mouse button on a node,
- Drags the node (mouse button is released all the time),
- Clicks again to place the node (left click to accept, right click to cancel the change),
- Using Esc button will cancel the selected vertex.
In QGIS 2.x the behavior is different, it is a drag-drop behavior, which means you need to drag the vertex while keep holding the left mouse and drop it on the target location:
- User presses the left mouse button on a node,
- Drags the node (with mouse button still being pressed),
- Releases the button to place the node,
- Using Esc button will not cancel the selected vertex.
You can have full information about the change in vertex tool with animated illustrations from here: Improved Node Tool