Markers are little symbols that can be added to the start of a path, to its end, and to the line in between those. They will be placed on the path’s stroke. This is very useful when you want to create arrows and diagrams quickly!
Markers will be located exactly on the nodes of the path. The start marker will appear on the first node of the path, the middle markers on each node along the path, and the end marker on the last node of the path.
Inkscape offers lots of different markers for you to choose from. You can look at them in the Stroke Style tab of the Fill and Stroke dialog, in the row labelled Markers. The left-most drop-down menu is for the start marker, the one in the middle for the middle markers, and the right-most one for the end markers.
Markers automatically take on the fill and stroke of the path they are attached to. In older Inkscape versions, the extensionwill do this for you.
If your arrows point into the wrong direction, you can change the direction of the path ().
List of available markers (TODO: insert image)