Be aware that the Altium documentation goes into much more detail than necessary for our purposes. The best way to determine what you don't know is to start a project.
Getting Started: http://techdocs.altium.com/display/ADOH/Getting+Started+with+Altium+Designer
Schematic Capture
When designing a printed circuit board (PCB), schematic capture occurs after deciding what functions the circuit must perform and selecting proper components to implement those functions. Schematic capture refers to the process of drawing out the circuit using schematic symbols to represent each component.
Schematic Editing Essentials - http://techdocs.altium.com/display/ADOH/Schematic+Editing+Essentials
Design Objects
These include any visible component displayed in the Schematic Editor. There are 2 types of Design Objects, Graphical and Electrical. They can be placed with LMB and rotated with Spacebar (http://techdocs.altium.com/display/ADOH/Schematic+Editing+Essentials#SchematicEditingEssentials-PlacingDesignObjects)
Graphical Objects - Lines, arcs, text, boxes
Electrical Objects - Parts 
, wires 
, buses, ports
Grids
For ease of navigation and object placement, interactive grids will lock cursors to their vertices. This is an important feature and should be properly configured to prevent misaligned components or missed electrical connections. To edit these grids, go to Tools >> Schematic Preferences.
There are 3 types of grids and they are used in both the Schematic Editor and the PCB Editor
Visible Grids - Adds a non-interactive visible grid to the schematic
Snap Grids - Locks the cursor to its vertices when placing/moving design objects
Electrical Grids - Ignores the snap grid and locks the cursor to its vertices when making electrical connections between design objects. Electrical Grids should be slightly smaller than Snap Grids.
More Details on Grids and Cursors - http://techdocs.altium.com/display/ADOH/Schematic+Editing+Essentials#SchematicEditingEssentials-GridsandCursors
Designators and Annotation
Annotation is the process of uniquely identifying every schematic symbol using designators - alphanumeric values. Each component designator can also be annotated manually, but it is much more preferred to use automated annotation tools at the end of schematic capture.
There are 3 methods to annotate a design, but we will focus on Schematic Level Annotation. This type of annotation will systematically assign designators to all selected schematic symbols, and can be accessed from Tools >> Annotate Schematics.
More Detail on Designators - http://techdocs.altium.com/display/ADRR/Sch_Obj-Designator((Designator))_AD
More Detail on Design Annotation - http://techdocs.altium.com/display/ADOH/Understanding+Design+Annotation
More Detail on Altium Front-End (Schematic Interface) - http://techdocs.altium.com/display/ADOH/Front-End+Design
Printed Circuit Board (PCB) Layout
A printed circuit board (PCB) is made up of an insulating fiberglass layer (usually FR4) with copper layers plated on either the top, bottom (single-sided), both (double-sided), or in between fiberglass layers (multi-layer). PCB layout is the process of transferring the schematic components and electrical connections onto a printed circuit board.
This process generally consists of 5 steps: determining the layer stack (how many layers, which layers are for what), placing each component (in a way that shortens connections and vias as much as possible), electrically connecting/routing all components using traces or polygons, design rule checking, and gerber creation.
The PCB Editor - http://techdocs.altium.com/display/ADRR/PCB_Edtr-PCBEditor((PCB+Editor))_AD
Moving Around - http://techdocs.altium.com/display/ADRR/PCB_Edtr-PCBEditor((PCB+Editor))_AD#PCBEditor-Panning
Design Rules - http://techdocs.altium.com/display/ADRR/PCB((Design+Rules+Reference))
Design rules are what defines the constraints (rules) for every aspect of the PCB. These rules are mostly distances between objects and will be discussed in more detail here. The design rules must follow the manufacturer's specifications and tolerances in order for the PCB to be made with as few errors as possible. The Design Rule Checking (DRC) tool is an automated way to check if your PCB has violated any of the design rules, and should be used throughout the PCB layout process, most importantly before gerber creation.
Other Topics
Schematic/PCB Synchronization
Guides - http://techdocs.altium.com/display/ADRR/PCB_Obj-SnapGuide((Snap+Guide))_AD