Three vertex roles, set separately
The Stroke row of the Appearance panel has a Markers section with Start, Mid and End. They are three independent properties, and mid applies to every interior vertex rather than to one - so a polyline plotting a data run gets a dot at every reading from a single setting.
Because markers are painted alongside the fill and the stroke, paint order decides which of the three lands on top - drag the Appearance panel rows to change it. That is the setting to reach for when an arrowhead is being covered by a thick stroke.
Five built in, or make your own
Arrow, Open Arrow, Circle, Diamond and Square ship with the editor and are marked "Built-in" in the Library panel's Markers tab; they are not editable, because their geometry comes from a shared registry rather than from shapes. The built-ins inherit the stroke color of the shape wearing them, so an arrowhead always matches its line.
For anything else, select shapes and use "Create Marker". The result is a definition whose contents are ordinary editable shapes - you can reopen it, change the geometry, and every stroke wearing it updates.
Orientation and scale are properties of the marker
A marker set to orient automatically turns to the path tangent at each vertex, which is what makes an arrowhead point along a curve rather than off it. A fixed angle instead keeps every copy at the same rotation, which is what you want for a tick or a label pin.
markerUnits decides whether the marker grows with the stroke. The SVG default scales with stroke width, so an arrowhead stays in proportion as the line thickens; the alternative pins it to a fixed size in user space. Both are attributes of the definition, so changing one updates every stroke that references it.
They export as real SVG
Markers leave the editor as <marker> elements in <defs> with marker-start, marker-mid and marker-end references - the native SVG 2 mechanism, handled by the browser. Nothing is baked into paths, so the arrowheads stay editable in whatever tool opens the file next.