I just want to know the basic formula of multiplayer combat..

How do I know which units will move first etc..

Example.. I tried to take worker from my opponent. I selected my warrior and clicked on worker to attack them.. but nothing happened for like 15 seconds. Then workers moved for one slot and my warriors followed after them. Why? Why haven't they attacked them earlier? Seems like they were waiting for them to move. And since I don't understand how this works I can prepare my strategy good enough. And that's my weakness.

Another example.
Friend of mine attacked my city ( he was intending to ). First my city shoot at one of his units. Then his 3 units had their turn while my units standing near the city didn't have a chance to move although orders were issued.

It's a little bit confusing. If you don't know which units will move first you can only guess what will happen you and can't adjust your strategy. Pls help. Thx in advance