The Shape Components can be used to create collision or triggers around other objects, indicate orientation or create paths.
Arrow Component
The ArrowComponent is a simple arrow rendered using lines and is useful for indicating which way an object should face. As seen in the door example below, the arrow indicates which way the door should face when placed in the level (as the door may be scripted to only open one way, the direction in which the arrow is facing).
The actual arrow will not show up in-game (unless the Hidden in Game option is unchecked) and the color and size can be adjusted as desired. This Component does not have any collision settings and could poentially also be used as a "marker" for your scripts (for example, adding an ArrowComponent to a CharacterBlueprint just above the characters shoulder, then when the player presses a button, having the CameraComponent move to the location of the ArrowComponent creating an over-the-shoulder style camera).
Box Component
A BoxComponent is a box generally used for simple collision (can also be used as a trigger as in shown in the example below).
A BoxComponent was added around a fire particle effect, with its collision settings set to Generate Overlap Events. When something overlaps the box, an event will be fired where you execute script that applies damage to the Actor that overlaps it. You could also set the Collision Response to BlockAll which would prevent all Actors from entering the box (if you wanted to keep things from entering the fire).
Capsule Component
The CapsuleComponent is a capsule shape which can also be used as simple collision (shown below) or as a trigger.
Above a CapsuleComponent is automatically included when creating a new Character Blueprint and provides the collision settings for the character, keeping them from intersecting with objects in the world. The CapsuleComponent can also Generate Overlap Events or Generate Hit Events to allow you to provide scripts for when either of those events occur.
Sphere Component
SphereComponents are spherical shapes that can be used for collision (ie. collision around projectiles as shown below).
Just as with the Box and Capsule Components, you can set the Collision Responses to generate the type of collision functionality you need.
Spline Component
A SplineComponent can be used to make streets or complex paths (in which other Components can follow). Below a SplineComponent, BillboardComponent and ParticleSystemComponent were added to a Blueprint with the intent of having the particle system following the defined path created by the spline.
Inside the Editor Viewport, you can edit the spline by Right-clicking on the Actor that has SplineComponent. This will bring up a context menu with options like adding points to the spline or defining the type of spline point to use. Below, a path was created to represent the outline of the Unreal Engine logo.
After providing some Blueprint script to update the location of the particle effect, the end result is represented below.
