There are two very useful sites on the board today. Both relate to operations but in a different aspect.
Site 1: The Operations SIG resources website
If you are new to the idea of model railroad (railway) operations then the OPSIG site is a great place to start. I will warn you though that there is a slippery slope downwards from here to building everything with an eye to operations after you’ve perused the pages. Plenty of fun stuff to learn about however, and all of it very well presented.
Site 2: A short course on railroading
I’ve only recently found this site. I’ve not finished reading it all yet, but what a fascinating read it is. Based on the notes and memories of L. E. Crowner and centering on the Union Pacific’s Los Angeles East Yard there is so much information here that you tend to lose yourself in the pages for hours.