Which size inner tubes to buy? New to cycling and have no idea what size inner tubes to buy for my particular bike.

Following dimensions on tire:


  N28x1.75*36H
  
  622*19c 


Seems to me this is an unconventional wheel size? Was on Wiggle and most tubes seem to be 700x25c.
The 622 x 19 is the rim size. 622 refers to an ISO 622 (700c or 29" in mountain bike parlance) wheel. 19 refers to the rim width in millimeters. 

The 28x1.75 is 700c x 45 tire size (or equivalently a 29 x 1.75). So, you need a tube suitable for this size. Tubes are sold by ranges, but it's not hard to find a 700c x 28-47c tube (this is what Schwalbe sells). You can also use tubes marked 29" x (some range containing 1.75). If you go to a bike shop and ask for either a 700c x 45 or 29x 1.75 tube, they should have you sorted out in a few seconds. 

The 700c = 29" thing is usually 700c for road/hybrids, 29" for mountain bikes but its the same wheel size. Confusingly, another name for 700c is 28". Why? Aliens.

As Criggie points out in the comments, make sure your tube has the right kind of valve. You could take your old tube to a shop and they'll sort you out. Or the bike.