Have to type .html at the end of my webpages

I recently noticed that for my fairly basic html and css coded site, you HAVE to type .html at the end of pages or they will not load. What is the easiest way to fix this nonsense?

Epic visual tool

Epson 5030UB 2D/3D 1080p 3LCD Projector Submitted March 27, 2016 at 12:56AM by intheaterssoon http://ift.tt/1MsClng