Navigating the Canvas

Zooming

To zoom the canvas you can use one of these methods:

Pinch-zoom when using an Apple magic trackpad.
Use the menu items in the View menu: Zoom In, Zoom Out, Actual Size, Zoom to Fit, and Zoom to Selection.
Use the keyboard shortcuts for these menu items: ⌘=, ⌘-, ⌘1, ⌘0, ⌥⌘0.
Scroll wheel zoom on a mouse, if Scroll wheel is set to Zoom in Settings -> General.
Scroll while holding ⌘ or ⌥ on a trackpad, or on a mouse if Scroll wheel is set to Pan.

Panning

To pan the canvas (i.e. scroll), you can:

Use the scroll bars if your Mac has them enabled in System Settings
Pan gesture on an Apple trackpad (two fingers) or magic mouse (one finger)
Scroll wheel pan on a mouse, if Scroll wheel is set to Pan in Settings -> General (the default). Hold shift to pan in the other direction, as is standard on MacOS.
Scroll wheel while holding ⌘ or ⌥ on a mouse, if Scroll wheel is set to Zoom.
Hold space and drag to pan.

Entering and leaving Editing Scopes

An Editing Scope is the container you are currently editing inside. For example, if you have made a Group of objects, you can edit inside the group (to edit the individual objects) by entering that group’s Editing Scope. Likewise, if you have drawn a Path, you can enter the path’s Editing Scope in order to move and edit the path’s points.

Entering an Editing Scope

Double click on the object in the canvas.
Double click on the row in the Layers palette. (But avoid the text of the name, as that would edit the layer’s name instead.)
Select a child object of the object, by clicking its row in the Layers palette. (You can’t select a child object directly by clicking on the canvas though, as that would select the outer object.)
Right click and choose Edit… from the context menu. The name of the menu item depends on the type of object, e.g. “Edit Path” or “Edit Group Contents”.
For Text objects, clicking on the text object with the Text tool active will enter its editing scope. A text object’s editing scope is how you edit its text.

Leaving an Editing Scope

Press the escape key when nothing is selected.
Click outside of the golden border on the canvas with the Select tool active.
Use the Scope Bar above the canvas to click on the parent item (e.g. the layer, which is always the first item on the scope bar).
Click on the scope’s parent, or some other object, in the Layers palette. This changes the selection, and the active Editing Scope follows the selection.

What’s on the canvas?

The canvas of your McKinley symbol contains the following things:

All the objects that make up your symbol!
A grid, if it is turned on via View -> Show Grid. You can control the spacing of the grid lines in settings.
Top and bottom capline/baseline guides. These are grey horizontal rules, and they show where the top and bottom of a capital letter would be in text alongside your symbol. They are fixed in place. If you change the size mode (via the toolbar, view menu or keyboard shortcuts), it moves the capline/baseline guides while leaving your symbol in the same place.
Left and right margin guides in blue. These ones are under your control. You can adjust them to accommodate the width of your symbol, and SF Symbols uses them to know how much space to leave when putting your symbol within text. You can change the margin guides separately per symbol weight if you use the floating Link Geometry control when the margin guide is selected.
Custom guides, which display in pink. Drag these out of the relevant ruler to create them.
A warning triangle in the bottom left corner, if there are currently any warnings for this variant. Click on it to open the Warnings palette.
HUD messages or controls (head-up display) in the bottom centre of the canvas. These might tell you that you are in a certain mode, or offer controls such as which part of a clipping mask you are editing.
Preview text, for you to compare the size of your symbol. The text displays in the San Francisco font with the same weight as the weight of symbol you’re currently editing. You can control what text string is used for previews, as well as turn it on and off, in the Document -> Appearance inspector pane. You can set the default text for new documents with Sample text in Settings -> Document Defaults.
A floating Link Geometry control, which appears when you have a relevant object selected. This allows you to change whether your edits will apply to all symbol weights, or just the current symbol weight.
Around the edge of the canvas are rulers, which show measurements (with an origin in the top left of the default symbol location in Small size, although of course you can change the location of your symbol by dragging the margin guides). You can also use the rulers to create guides, as mentioned above.

Things that control how the canvas looks

In Inspector -> Document -> Appearance, you can choose the canvas colours. “System” causes it to follow the system light/dark mode appearance; or you can force light or dark mode, or you can choose Custom to choose all colours yourself (including the canvas background).
The canvas displays the currently active weight, colour mode and symbol size. You control all of these through the toolbar:

toolbar-modes

(There are also associated menu items and keyboard shortcuts for all of these, in the View menu.)

You may see onion skins on the canvas, if they are enabled. Onion skins show the position/size of objects on other symbol weights, so you can compare them to the current weight you are editing. You can turn onion skinning on and off via a toolbar button or via View -> Onion Skin -> Show Onion Skin. You can also choose whether onion skins show up for just the selected object (On Selection), or for all objects all the time (Always).

Things that control how the canvas works

Smart Guides are automatic snap points for when you’re creating or dragging objects. They’ll snap to other lines, other guides, centre points of objects, etc. Turn them on/off in View -> Snap to Smart Guides.
If you turn on Snap to Grid via View -> Snap to Grid, then object creation and dragging will snap to the visible grid. This will follow the spacing of grid lines that you have set in Settings.
There are some other settings that control how selection and editing works: see the relevant Help page for more details.