An Actor is any object that can be placed into a Level, such as a camera, Static Mesh, or player start location. Actors support 3D transformations such as translation, rotation, and scaling. They can be created (spawned) and destroyed through gameplay code (C++ or Blueprints).
In C++, AActor
is the base class of all Actors.
To create a Level, you place Actors into a Level (map), then move and scale them to create an environment, and add script to make them behave the way you want. This section covers the basic techniques of working with Actors, such as placing, selecting, and transforming Actors. It also covers some of the most commonly used Actor types.
Working with Actors
Placing Actors Shows how you can place Actors such as props, lights, and cameras into your Level. Selecting Actors Overview of methods available for selecting Actors in the Level Editor viewport. Transforming Actors How to modify the location, rotation, and scale of Actors in a Level. Actor Snapping Overview of Actor snapping in Unreal Engine. Actor Mobility Setting that controls whether an Actor can move or change in some way during gameplay. Grouping Actors How to create and work with groups of Actors in Unreal Engine. Merging Actors How to merge two or more Static Mesh Actors into a single Actor in Unreal Engine.
Common Actor Types
This is not a comprehensive list of every Actor type available in Unreal Engine. Some plugins and project templates add their own Actors, and certain Actors may not be available for all projects.

Physics Volume Actor
Describes the properties of Physics Volumes in Unreal Engine.

Static Mesh Actors
Place Static Mesh Actors in your Level to create your game world.

Skeletal Mesh Actors
Use Skeletal Mesh Actors to create player avatars and populate your game world.

Geometry Brush Actors
Guide to using BSP brushes to create level geometry in Unreal Engine.

Camera Actors
Understanding the fundamentals of Cameras in Unreal Engine.

Audio Volume Actor
Audio Volume reference details

Player Start Actor
Use Player Start Actors to set up starting locations for players.

Trigger Volume Actors
Actor that can be activated and cause events to occur in the Level.

Volume Actors
Reference for the different kinds of Volume Actors in Unreal Engine.

Pain-Causing Volume Actor
Pain-Causing Volume reference details

Decal Actors
A guide to using the Deferred Decal actor.

3D Text Actor
Guide to placing 3D Text and using it to create motion graphics.

Target Point Actors
Guide to creating and using Target Actors.