Invasion of the Giants

The chapter II ability goes on the stack without a target. You choose whether to reveal a Giant card from your hand after you have drawn a card. When you do, the reflexive triggered ability triggers. This is different than effects that say "If you do" in that players can respond after you've revealed the Giant card but before damage is dealt.

If multiple chapter abilities trigger at the same time, their controller puts them on the stack in any order. If any of them require targets, those targets are chosen as you put the abilities on the stack, before any of those abilities resolve.

As a Saga enters the battlefield, its controller puts a lore counter on it. As your precombat main phase begins (immediately after your draw step), you put another lore counter on each Saga you control. Putting a lore counter on a Saga in either of these ways doesn't use the stack.