The lead dropcap is created by adding this specific markup to the text tab in the post editor like so:

<p class="lead dropcap">Toffee sugar plum carrot cake biscuit chupa chups. Oat cake carrot cake lollipop carrot cake oat cake biscuit applicake. Dessert cheesecake caramels dragée soufflé cookie muffin tart gummi bears.</p>

Let me know if that helps.