The two parts that are included in an Anchor Base activity are Anchor and Action. The Anchor Base activity is a container that searches for a UI element by using other UI elements as anchors. This should be used when a reliable selector is not available. The Anchor Base activity has two sections: Anchor and Action. The Anchor section contains an activity that identifies the anchor element, such as Find Element or Find Image. The Action section contains an activity that performs an action on the target element, such as Click or Type Into. The Anchor Base activity also has a property called AnchorPosition, which specifies the relative position of the target element to the anchor element, such as left, right, top, or bottom2. For example, if the Anchor Base activity is used to click on a button that is always to the right of a label, the Anchor section can use the Find Element activity to find the label, the Action section can use the Click activity to click on the button, and the AnchorPosition property can be set to Right3.
References: Anchor Base and How to properly use AnchorBase activity? from UiPath documentation and forum.