How do I set an offset between two strokes?

To set an offset measurement:

Activate the Precision menu on canvas.
Turn on Measure.
Select your stroke(s), and tap Duplicate on the selection popup (the two stacked squares icon).
When you start dragging the duplicate, you’ll see it shows an offset measurement from the original stroke. Tap the measurement label and it will remain on screen after the stroke is deselected. It doesn't have to be an exact amount, you can edit the offset after setting the label.
To edit the offset to a specific amount, tap+hold the measurement label to bring up a keyboard. Enter your measurement and the offset will be updated between objects.