Step 1. In the dashboard click 'LISTS' and choose List Actions - New Segment as shown below.
Step 2. Name your segment and then choose Create segment based on a List
Step 3. Adding your conditions
Choose +Mailed, Opened, Clicked Conditions. This will add a condition statement where you can choose from the drop down and fill in Have Opened and then fill in the time frame. For this example I chose 180 days.
I added Have Clicked as well in this example because a clicker can open an email without it tracking it as an open so its always good to add that as well.
What you will want to make sure of is if you want ANY of these conditions vs matching them ALL you will need to select Match: ANY. If you put ALL then the condition will need to be met on both items. In this case they would need to have opened and clicked vs Opened OR clicked. Its a big difference so make sure you select the correct conditional for Match.
You will need to select your lists that you want to run your conditions against. Once that is done click 'SAVE SEGMENT'.
Thats it! You're done creating an Opener Segment. That was easy wasn't it?