The header code looks like this:
<ul class="nav nav-tabs">
<li class="nav-item">
<a href="#rent" class="nav-link active" data-toggle="tab">Rent</a>
</li></ul>
The content for that header looks like this:
<div class="tab-content">
<div class="tab-pane fade in active" id="rent">
<p>Content goes here!</p>
</div>
</div>
Obviously, you would just replace "rent" with whatever name you want to use.
With the release of K2 2.9, things get even easier, since we can now embed a K2 Extra Field name or value in a K2 template with one line of code:
<?php echo $this->item->extraFields->ExtraFieldName->value; ?>
Now we simply have to replace "Content goes here!" with the Extra Field snippet:
div class="tab-content">
<div class="tab-pane fade in active" id="rent">
<p><?php echo $this->item->extraFields->Rent->value; ?></p>
</div>
</div>
The whole block looks like this:
<?php if($this->item->params->get('itemExtraFields') && count($this->item->extra_fields)): ?>
<!-- Item extra fields -->
<div class="itemExtraFields">
<ul class="nav nav-tabs">
<li class="nav-item">
<a href="#rent" class="nav-link active" data-toggle="tab">Rent</a>
</li>
<li class="nav-item">
<a href="#floorplan" class="nav-link" data-toggle="tab">Floor Plan</a>
</li>
<li class="nav-item">
<a href="#pets" class="nav-link" data-toggle="tab">Pets</a>
</li>
<li class="nav-item">
<a href="#walkscore" class="nav-link" data-toggle="tab">Walk Score</a>
</li>
</ul>
<div class="tab-content">
<div class="tab-pane fade in active" id="rent">
<p><?php echo $this->item->extraFields->Rent->value; ?></p>
</div>
<div class="tab-pane fade" id="floorplan">
<p><?php echo $this->item->extraFields->Floorplan->value; ?></p>
</div>
<div class="tab-pane fade" id="pets">
<p><?php echo $this->item->extraFields->Pets->value; ?></p>
</div>
<div class="tab-pane fade" id="walkscore">
<p><?php echo $this->item->extraFields->WalkScore->value; ?></p>
</div>
<div class="tab-pane fade" id="map">
<p><?php echo $this->item->extraFields->Map->value; ?></p>
</div>
</div>
</div>
<?php endif; ?>
You can see this in action here.
If you need help coding a custom K2 template to put your Extra Fields in tabs, contact me and I'll be happy to help!