There's some sort of timer, you wait until a messenger comes with a report and you'll be asked for instructions on how to proceed and you get three choices that boil down to
1. The Right Option
2. The Wrong Option
3. Ask Apple
And the wrong option is usually pretty obvious. Shu will pretty quickly take over the Greenhill battle regardless of what you do so you're left with directing the army at the Muse border. 1 or 2 reports after that Hauser will report that they've driven off the reinforcements at the border, if you kept choosing the wrong options the report also says that Viktor got surrounded during the battle and one of the non-essential characters died as a result of your reckless orders.
Shu will then request that you come to Greenhill as Highland has retreated beyond the walls.
Not aware of any videos but there's a Let's Play archive that brushes over all the three options https://lparchive.org/Suikoden-II-(by-T ... date%2050/