A Five of a Kind is made up of five cards of the same nominal rank (say, 5 Kings). However, since you can only ever have 4 cards of the same rank in any deck, this hand can be played strictly when you're playing with Jokers. This is the highest possible hand in the entire game, and it is also the rarest.

For example, here's a Five of a Kind of Kings:

A Royal Flush is a hand made up of 5 highest-ranking cards in a row of the same suit; that is, an Ace, a King, a Queen, a Jack and a Ten.

A Joker can enter into play here by replacing any of these cards in order to complete the Royal Flush for the player.

For example, here's a Royal Flush of spades where the Joker is replacing the Queen:

A Straight Flush involves any five cards of the same suit ordered subsequently by rank (except for the Ten-to-Ace sequence, which is the Royal Flush described above). An Ace may both start and end the sequence; that is, a Straight Flush of Ace, Two, Three, Four and Five is a valid hand.

A Joker may be used to replace any card that makes the rank of this hand the strongest possible.

For example, here's a Straight Flush ending with a Ten, where a Joker is used to replace a Ten rather than a Five:

A Four of a Kind (sometimes also called Quads) is a hand made up of four cards identical in rank + a kicker card.

A Joker can be used to replace any of the four cards needed to make up a complete Four of a Kind.

If a player has a Three of a Kind hand, it is automatically upgraded to a Four of a Kind with a Joker's help (and not to a Full House).

Here's an example of a Four of a Kind of Jacks:

A Full House is a hand of three cards identical in rank + a One Pair.

A Joker upgrades a Two Pair to a Full House. And it takes on the role of a card that upgrades the stronger of the Two Pair hands to an identical triple.

Here's an example of a Full House with three Aces:

A Flush is simply a hand made up of five cards of the same suit; they don't have to be ordered.

A Joker can be used to replace a card that will make the rank of the Flush the highest. Usually it will be used as an Ace, but if there's an Ace already available from the other regular cards, then it goes on to replace a King, and so on.

Here's an example of a Flush of clubs ending with an Ace:

A Straight is a hand made up of five cards of any suit, but ordered subsequently by rank.

Here, an Ace can both start and end the sequence; that is, a Straight from an Ace to a Five is playable.

A Joker can be used to replace a card that makes the rank of the Straight the highest possible.

Here's an example of a Straight ending with a Six, where the Joker represents a Six rather than an Ace:

A Three of a Kind (sometimes called Trips) is a hand made up of three cards of the same rank + two other kicker cards.

A Joker always upgrades a One Pair to a Three of a Kind.

Here's an example of a Three of a Kind of Tens:

A Two Pair is a hand made up of two pairs of cards of the same rank (but different between the two pairs) + a kicker card.

A Joker cannot be used to put this hand together, since if a player has already got a One Pair on her hands, a Joker will automatically upgrade it to a Three of a Kind, which is a stronger hand to play than a Two Pair.

A One Pair is a hand made up of two cards of the same rank + three other kicker cards.

If a Joker is used to upgrade a hand with just a High Card, it automatically upgrades that hand to a One Pair. In this case, the Joker acts as a card of the same rank as the highest regular card available to the player, thus forming a pair with it.

Here's an example of a One Pair of Tens:

A High Card is the lowest hand playable in Texas Hold 'Em. It involves no matches and is simply about five unordered cards, where the highest-ranking one determines its strength and the other four are kickers.

You cannot use a Joker to play this hand, since it automatically upgrades it to a One Pair.