Alright, with that out of the way, I can go into a bit more detail.
So Guild Order can be thought of as a extra high powered advent in terms of play, but with a different reward structure.
5 stages instead of 3. Grunts vary from mid 6 digits to ~1.2 million HP. 3rd stage is a mini-boss with 3 million HP. The boss at the end has high 7 digits HP.
Instead of costing AP/BP/whatever, you're limited to one attempt per day.
Instead of farming materials to exchange for, you're trying to satisfy missions (each week has a set of 10 missions; each GO lasts for 2 weeks for a total of 20 missions). Clearing X number of missions for a given GO gets you so and so rewards. The main prize that sticks out here would be orichalcon, which can be used for final limit breaks or to be exchanged for stuff.
The key breakpoints for rewards (ie at which points are the ori given) are 6 (ori #1), 10 (ori #2), 18 (ori #3), and all 20 (ori #4 and 5).
6 mission points requires a minimum of being able to clear stage 2. That would mean the following missions from week 1: attempt 3 times, attempt 5 times, clear stage 1 3 times, clear stage 2 3 times. Then from week 2: attempt 5 times, clear stage 2 times.
10 mission points require being able to satisfy at least one of the missions that specify clearing the whole thing under X condition, because there are exactly 9 missions that don't require clearing.
So once you can actually try Guild Order, you can give it a shot. Attempting won't cost you anything. But you're new; if you fail, don't worry about it. It'll be a while before you're 'expected' to be able to consistently farm ori.