How to split test on GoogleAds - Duplicate Ad?

Dear marketers,

I’m going through Module #9 - Split testing and data analysis
And I feel lost at Testing with Google Ads.

Here’s the situation:
So if I have 2 landing pages - everything is the same, just headlines changes
I’ll have 2 URL destinations for presell pages.
So I make 2 Ads, one with each Presell Page URL.

These 2 ads should look the same? (duplicated, everything the same i just change URL destination)
or change words that are congruent with the headline of the presell page?

I used to make this possible mistake. I duplicated the Ad, and just changed the destination URL.
Then google went ahead and compete with my own ad, if i have 2 identical ads?

It’s a blessing to see this “AD Rotation | Do Not Optimize - Rotate Ads Indefinitely”
This assures 50% of traffic goes to each ad. Right?

Hopefully someone knows this better and light me the way.