I tried to follow a service with my orthodox Portuguese siddur at a conservative congregation service and I couldn't. What is the difference between a conservative and an orthodox Sidur?
You mentioned that you prayed from an Orthodox Portuguese siddur. I am not an expert in the customs of Portugal, but I'm going to assume your siddur was in some form of Nusach Sepharad. (And possibly is a De Sola Pool siddur?)
If that is the case, then you might have difficulty following the service even within an Orthodox congregation, if the prayers there were Nusach Ashkenaz! (And many Orthodox congregations in America do indeed use Nusach Asheknaz.)
I do not have room text box (or time in general) to outline all the differences between Nusach Sepharad and Ashkenaz, but some differences include the orders of the morning blessings, textual differences throughout the prayers, etc. Additionally, there are differences between different siddurim all claiming to be of the Sepharadi nusach! Different Sephardic communities across the globe had different traditions regarding the prayers, so the Portuguese nusach might be different from the Syrian or Moroccan nusach.
As for the Conservative siddur, the Conservative nusach is entirely Ashkenazi in nature, although you can see the differences between an Orthodox siddur and Conservative siddur here.
And, if you are unfamiliar with the word "nusach", or what I mean when I say Nusach Sepharad, Ashkenaz, etc., then please see here.