As you place them (with the second card face up on the top of the pack on show) you make sure that they are protruding over the inner end of the pack by about 1 cm. At this point you name the card to your audience then grip the two top cards in the same manner as before using the thumb and first finger of the right-hand below and above respectively and you turn the two cards face down on top of the pack flush.
This particular sleight of hand has many different uses, one of the most obvious is that you can apparently show the top card then place it in the middle of the pack and it immediately appears to return to the top.
The double lift sleight of hand is one of the most popular and well established sleights in the whole repertoire of card manipulation. This is proven by the fact that it has been around for well over 200 years. It was first published in 1776! You can read more on Wikipedia’s page.
The great card magician Dai Vernon was known for performing the double turnover – an extension of the double lift sleight of hand.