Sketch’s canvas is infinite in size. You can view the canvas both in a resolution-independent view where you have infinite precision, or you can turn on Pixel Preview and you will know exactly how every pixel will look on export.
If you’d like to define a fixed frame inside the infinite canvas, simply create an Artboard using the Artboard tool.
Navigating around the canvas is easy. You can use the scroll-wheel on your mouse or the trackpad on your MacBook to scroll in either direction. You can also hold down the spacebar and click and drag to pan around as well.
Lastly, if no object is selected you can use the arrow keys to pan the canvas as well.
Note that Page Up / Page Down switches between Pages.
Apart from that there are various shortcuts in the View menu for zooming in and out to specific content. You can also hold down the ⌘ key an use the scroll wheel on your mouse to zoom in and out as well.
Lastly, you can use the Z key to quickly zoom into a particular area. Click and drag anywhere on the canvas to zoom the viewport into that area..