The Turn button is in the lower left corner. If you haven't finished your turn it won't show up, That was my idea for Galactic Civilizations 3, so if you want to blame anybody for that it is my fault. I think it was a good idea. If you don't want to do anything on the planets there is an economic, or other project you can do that on the planet. You can even set it to repeat, but I don't understand why anyone would do that. You could set your shipyard to not do that it is in your left corner just check it. Any of you ship you don't want to move just order them to guard.

Do the items listed in the button one by one.

If you have "idle ship" when you click the button, it will take you there and you can move the ship or hit "spacebar" to do nothing.

If you have "idle shipyard or planet" click on the button and it will take you there to select something to do.

In general, you'll get more options for the shipyards/planets as you research more techs

Does that help?

bottom right of the screen