You create layout for FMGo in the same manner you do for FMP, you changed based on the screen size. Scripts are used to detect the device the database is running and then Go to the layout based on the device detected. The start up solutions use this method in the startup script. PhilModJunk has / had (I guess they are still there) some tips about creating apps on the FMGo forum. I don't know if he has updated it since FM13 has came out, but you could do a search of the forum.
Here's the link: An Old Dog learns some new tricks...
It could use an update but is still fairly relevant. Also keep in mind that we have a section of this forum specifically dedicated to FM GO that you can use to post questions.
Probably the biggest change in what I do from when I first posted those comments is that I now have both an iPad and an iPhone 6. With screens that are both larger and with many more screen sizes, I don't rely on using auto-size anchors to "slide" things out of hiding when the device is rotated from portrait to landscape orientation. I just use two layouts--each customized for one orientation or the other and use a script trigger performed script to change layouts when the device is rotated.
I also find popovers much nicer and a very good interface design tool for use on iOS devices as I can actually design the popover to be taller than the device screen and then the user can use gestures to scroll the entire popover contents up or down as needed.
Thank you Stacy, Phil, armed with that I think I am off to a great start!