This is a great game to play with teenagers or older children. Any number of people can play, but it can be a little slow with just 2 (possible though).
You need to have a different deck of cards for each player (with a different pattern on the back of each).
I buy my playing cards from the dollar aisle at the craft store. All the "official" cards cost $4 or $5 per deck. That's too much for me, and the craft store has cooler patterns (zebra stripe and harlequin) I keep them on an urn in the middle of the table.
Pardon my ugly pictures here.
Ok, this is a bit like group Solitare. To get ready to play, each person places 4 cards face up (the River), makes a pile of 13 cards with the top card face up (the Nertz pile), and the rest are in a pile on the left (the Stream). The goal of each round is to be the first player to get rid of the Nertz pile. The player with the highest number of points wins the game.
The photos show a game for 4 people with 4 different decks of cards.
Everyone starts playing at the same time. After you get the hang of it, the game can get really fast.
Your goal is to get the cards off the Nertz pile. You do this by playing them into the River or the Lake. The cards in the River (like Solitare) are stacked with high cards (top) to low cards (bottom) alternating red and black and can be different suits. The Lake is where everyone can play off anyone else's cards. These are piles (like Solitare) starting with the Ace and building on top of that with the next highest card number of the same suit and color. If you play a card from the Nertz pile, you flip over the next one and try to play it. You can also move cards from the River into the Lake.
If you get stuck, you go to your Stream pile (like Solitare). You flip 3 cards from the Stream pile over. When you can't play any of those, flip 3 more over.
The first player to get rid of their Nertz pile calls out "Nertz" and play stops. Separate all the cards in the Lake by type of deck so each player can count how many they played into the Lake (don't mix them up with the others). Each player's points are the total of their cards played into the Lake minus how many cards they had left in the Nertz pile (Stream and River cards are not counted). The person who called Nertz gets a 10 point bonus.
We usually play to 200 points. You can play with teams, but I've never tried that. If my instructions make absolutely no sense to you, or you would like to read more detailed instructions on how to play, go to the Official Nertz Rulebook at Playnertz.com.