Flip for who goes first. Then work your way up from onsies to tensies and back down to onsies. Begin by throwing the jacks out on the floor. Then, taking a ball, (you can use the little ones that come in the sets or the "pinkies" (tennis-ball sized pink rubber balls) you throw the ball into the air, pick up the correct number of jacks and letting the ball bounce once, catch the ball while still holding the jack(s). You can only use one hand. Your turn continues until you miss the ball, miss the jacks, move a jack, or drop a jack you've just picked up. Then you are out and it is the next person's turn.
For instance, on onsies, you pick up one jack at a time, until you've collected all ten. (You may put the jacks you've collected into your other hand or on the ground before you try to collect more). On twosies, you pick them all up two at a time. On threesies, you pick them up three at a time, with one left over. You pick up the leftover(s) by itself. If you pick up the leftover before you've picked up all the evenly grouped jacks, you are putting the horse before the cart and therefore must call "cart" as you take the leftover jack(s). On foursies, there are, obviously, two groups of four and two jacks in the "cart." Fivesies has no cart. Sixsies has one group of six and four in the "cart." And so on.
If you throw the jacks and two (or more) are touching it is "kissies" and you have the option of picking up the kissing jacks and dropping them to spread them out. This is sometimes advantageous; sometimes not.
Players need to know about flipping. By flipping, it is meant that you take all the jacks in the palms of your two hands held together, throw them into the air as you turn your hands over so that the backs are now upwards with index fingers touching to form a surface onto which you will catch the jacks. Now, throw the jacks into the air again, this time returning your hands to the palms up position at which you started. Catch all the jacks? Good. When flipping for first, the player who drops the least goes first. If none drop, the you take turns flipping until someone drops one, determining who goes first.
You may also decide to flip at the beginning of a game. Flipping is done on your first turn only, and only until you drop a jack. The level at which you drop the jack(s) must be played from those dropped jacks. You continue from there. Thus, if you drop 2 jacks on your third flip (threesies), you would have to pick up the two jacks together (since at threesies you are taking them three at a time) and then continue with foursies. How far you can flip is decided at the outset of a game:flip only to fivsies, flip to tensies, flip all the way, and no flipping.
"Fancies" are specialty jacks rounds. At the start of a game, the players will decided how many and what kinds of fancies will be included. There was a huge collection of fancies that were just common knowledge when I was a kid. Some fancies are short: a simple chant with a certain pattern of activity that composed the whole fancy. Some fancies are long: a certain, trickier way of picking up the jacks that was performed from onsies to tensies. Thus a game might be agreed upon: "Flip to tensies. Five fancies; two long, three short." meaning players can flip as far as tensies, but must play tensies back to onesies no matter what, then complete two long fancies and three short fancies in order to win.