Open your Google Slides presentation.

Click on "View" in the top menu.

Select "Zoom" and choose a zoom level (50%, 100%, 200%, etc.).

Use the zoom tool (magnifying glass icon) from the toolbar.

Click on the slide to zoom in or out.

Use "Ctrl" (Windows) or "Cmd" (Mac) with "+" or "-" for quick zooming.

Reset zoom by selecting "Fit" from the zoom options.