I am trying to work with styled strokes. Simple dashed strokes.

What the numbers in the "Pattern" field represent? I couldn't find any explanation about those numbers? What is the format and how it should influence the style? Attached screenshot...

This is a repeating pattern in your dashed stroke. The first digit is the length of a dash. The second is the length of a gap. Third is a dash, fourth is a gap, etc. Set as many dashes and gaps as you want. 

I'd add that digits refer to dash length in term of line width.

The choice of line cap modifies the gap space, for the same settings 3 3 for example.