Like in Diamond & Pearl, there is an item called Honey that you'll be able to find within the game. You will first encounter this in the Floaroma Meadow after you save a man from a Galactic Grunt. He will give you 10 items of Honey to tide you over. From there, you can buy more Honey in amounts of 1s or 10s for 100 a piece. You can also obtain it with Pokémon with the Honey Gather ability

Honey Trees are the method on which you can place the Honey. After you place the Honey on a particular tree, return to it in six hours and the tree should be rustling. It has a Pokémon on it that you can now battle. This Pokémon is decided when you apply the Honey to the tree, however you will have the ability to reset in front of the tree to get the gender of Pokémon that you want. So if you want a female Combee or a Male Burmy, you'll be able to reset here until you get one. Here are the locations of the Trees throughout Sinnoh;

• Route 205
• Route 206
• Route 207
• Route 208
• Route 209
• Route 210
• Route 211
• Route 212
• Route 213
• Route 214
• Route 215
• Route 218
• Route 221
• Route 222
• Eterna Forest
• Floaroma Meadow
• Fuego Ironworks
• Valley Windworks