Complex sentence: The mechanic's grip is a basic method to hold the cards that allows you the ability to do more with the cards like and easy view of the top card's face or the ability to lift and select a card without the spectators knowledge.
Split into simpler sentences: The mechanic's grip is a basic method of holding the cards, that allows you to do more with the cards. This method allows you to view of the top card's face or lift and select a card without the spectators knowledge.