Following a BLine (the very old way)
File > New Time tab > End Time > 10s > OK select the BLine Tool enable just the Outline checkbox draw a bline that you want the arrow to move along select the new bline layer, go to its parameters right-click on the vertices parameter and "export" it it will ask for a name. you can use whatever name you like but for this tutorial I'm calling it "path" (note that you could have checked the 'auto export' box in the draw tool, and set the name in the text box at the top of the tool options to save having to chose export from the menu - it doesn't matter which you use) switch back to the 'Normal' tool and look in the "Children" dialog. expand the ValueBase Nodes and you'll see all the things that have been exported. selecting them will allow us to re-use them elsewhere in the animation later
back in the bline tool, enable Fill and Outline checkboxes in tool options draw an arrow or whatever, pointing to the right select the outline, hit control-a to select all its ducks except the green position duck drag the ducks so that the arrow is centred around the green position duck add a rotate layer above the outline and region encapsulate the rotate, outline, and region layers rename the encapsulation layer "arrow"
so now you've got 2 top-level layers: a curved path, and an encapsulation containing an arrow and a rotate layer
select the "arrow" encapsulation layer we want this layer to move along the "path" bline. the Origin parameter of an encapsulation layer can be used to move everything it contains right-click the Origin parameter and select Convert > BLine Vertex the Origin parameter will now be expandable - click the small triangle to its left to expand it the Origin of the "arrow" layer is now defined by 3 sub parameters: a BLine, the amount to travel along the BLine, and a checkbox that we'll ignore for now. in the Children dialog, select the "path" ValueNode then in the Params dialog, right-click on the "arrow" layer's BLine sub-parameter and "Connect" it to the selected "path" value the arrow will move so that it is about half-way along the BLine path (because the Amount sub-parameter defaults to 0.5). edit the Amount sub parameter to 0 and to 1, and see the arrow moves to one end of the path and then the other. the "Loop" sub parameter determines what happens if you use a value outside the range 0-1 for the Amount. If "Loop" isn't checked, values less than 0 count as 0 and values greater than 1 count as 1. If "Loop" is checked, the value wraps around, so Amounts of 2.4, 1.4, 0.4, -0.6, -1.6, etc all act the same.
So we've got the arrow moving along the line, but only if we manually edit the Amount parameter. Let's get it to move automatically, by converting the constant Amount parameter into a linearly changing value.
Right-click the Amount parameter, and Convert it to Linear. This adds sub parameters Rate (how fast the value goes up, per second) and Offset (what value it has at time zero). Set Rate to 0.1 and Offset to 0. That will make the value of Amount be 0 at time 0 and 1 at time 10s, so the arrow will move from one end of the line to the other throughout the course of the animation. This linearly changing value of the Amount parameter will be useful later on, so let's export it into the Children dialog so we can find it easily later. Right-click the Amount parameter and Export it as "engine". I call it "engine" because this is the parameter that drives the animation.
Try File > Preview or View > Play to watch the animation. If you like, play with the sub-parameters - turn the Rate up to 0.25 and turn on the Loop checkbox and watch the preview again. You'll see that the arrow moves 3 times faster than before, reaching the end of the line after 4 seconds. Turning Loop on means that it will then reappear at the start of the line, and keep moving. Not having Loop on would make it stay at the end of the line until the animation stopped.
You'll notice that although the arrow moves along the line, it doesn't rotate to face the direction of travel. But that's what we're going to use the Rotate layer for. Open up the "arrow" encapsulation layer and select the Rotate layer inside. Right-click the Amount parameter, which specifies the amount to rotate, and Convert it to type BLine Tangent. Open up the sub parameters, select the "path" value in the children dialog, and connect it to the rotate layer's BLine sub-parameter, and select the "engine" value in the children dialog and connect it to the rotate layer's Amount sub-parameter.