Complex sentence: KLM offers various check-in methods to its passengers, who can check in for their flights at self-service check-in kiosks at the airport, via the Internet, or via a mobile telephone or tablet.
Split into simpler sentences: KLM offers various check-in methods to its passengers. Passengers are able to check in for their flights at the self-service check-in kiosks at the airport, via the Internet, and via a mobile phone or tablet.