I want to make the icosphere grow as it moves along the length of the curve. I figure I need to know the length of the curve to do that correctly. I have no idea where I’m supposed to plug in this Spline Length node. Why the hell can’t I plug the curve INTO the spline length node to find out the length?
You need to plug both the spline output and the attribute you want into one of the Attribute nodes. The Attribute Statistic node, for example, outputs the raw values. Check its help page to see what the different outputs do.
You can also set it up like this. The first image shows if your curve has only a single spline whereas the second image shows how to set it up if you have multiple splines but only want to use a single one.
You move the object with the green node and select the spline with the red node.