Naturally, everyone - and babies in particular - will develop sleep associations. These are the things that you associate with bedtime, and allow you to create an environment in which it is easy to fall asleep. When your baby is at an extremely young age, he will naturally develop sleep associations involving the mother, as he will often fall asleep in her arms. As you attempt to get your baby to sleep in his own, however, it is crucial that you work to change these associations.
If you always put your child to sleep by holding him, or allowing him to use a pacifier, you create a sleep association with these things. Then, when your child wakes up in the middle of then night, he can't go back to sleep on his own because he is unable to recreate his sleeping environment without you: he needs you to feed him or rock him in order to sleep.
As you begin to try and get your child to sleep on his own, you should introduce items into his sleeping routine that he can sleep with, such as a particular blanket or a stuffed animal. What this will do is create associations for your child with these items for sleep. Then, when he awakes in the middle of the night, he will be able to recreate a sleeping environment without your assistance by grabbing his stuffed animal, etc. It can also be beneficial to introduce "transitional items" into your baby's bedtime routine: Allow him to have his stuffed animal or blanket with him during a final feeding and before-bedtime activities, and allow him to take these things with him to bed.
No matter what you do, your child is going to be creating his or her own sleep associations. Your job is to try and create associations with items that are under his or her control. By giving your child as much control over his sleeping environment as possible, you allow him to begin to achieve sleep independently. The most difficult transition in early parenting is the one towards independent sleep for your child, and if you introduce new items into your child's sleeping place, you will hasten this transition, which will soon allow both you and your child to get a good night's rest.