Open a file or paste the code
Drag an .svg file onto the canvas, or use File > Open... (Ctrl+O). On an empty drawing the file becomes the document, with its own width, height and viewBox, and the view zooms to fit it. The same door opens Adobe Illustrator .ai and .eps files and PDFs, page by page; the Illustrator import page and PDF to SVG cover what those carry over.
Have the code instead of a file, from a web page, a code editor or an icon library? Copy the markup and press Ctrl+V on the canvas, or use Edit > Paste SVG Markup… and paste it into the box. The SVG is added to the drawing as shapes you can click on. Markup that is not valid XML is not guessed at: the dialog says what is wrong and, where the parser reports it, the line and column.
Play and inspect SVG animations
An animated SVG opens paused, so you can look at any frame. Press Ctrl+Enter, or choose Window > Interactive Preview, and the file runs the way a browser shows it: SMIL animations play, and animations that begin on a click start when you click the element. Press Escape to return to editing.
To step through the motion instead, open the Animation tab at the bottom of the editor and use Animation > Play/Pause, or drag the playhead to any moment. Every animated property is a track on the animation timeline, with its keyframes laid out in time.
Inspect SVG elements and attributes
Press F12 for the XML Inspector. It shows the document as elements and attributes, and you can change or remove an attribute right there. The Elements panel lists every shape and group, so an element hidden behind another is one click away.
Select a path to read its geometry: the Path Editor panel shows the d attribute as text and as one row per command.
Review import warnings
When a file uses an element the editor does not support, the import finishes with a warning that says how many things were left out, instead of quietly drawing less. An Illustrator or PDF import also keeps a full report under File > Last Import Report...
Scripts inside an SVG are kept in the file and written back out when you export, but they never run in the editor, so opening a file from an unknown source runs none of its code.
Zoom in on the detail
View > Zoom In (Ctrl++) and View > Zoom Out (Ctrl+-) step the zoom, View > Reset Zoom (Ctrl+0) returns to 100%, and View > Zoom to Fit All Objects frames everything in the drawing. The drawing is vectors at every zoom level, so hairlines and small text stay sharp.
Keep a copy as an image
Open the Export panel (Ctrl+Shift+E) and choose PNG, JPEG or WebP to save the SVG as a picture at 1x to 4x or an exact pixel size, free. How to convert SVG to PNG walks through the settings, and the SVG converter page lists every format.