Once you have your yarn its time to figure out your needle situation.
If you are a beginner buying your first set of knitting needles can seem just as confusing as the wide world of yarn. There are so many types of needles, straight needles, circular needles, and double pointed needles. These are all made in just as many materials, wood, bamboo, steal, and acrylic. And these all come in sizes ranging from US 000000 to US 32. With so much variety it can make your head spin.
If you were successful in finding a single ply worsted weight yarn you are going to need about a size US 8 to a US 10 needle. Checking your yarn's label is also helpful because there will be a suggested needle size printed there. These are usually pretty good recommendations.
Which type of needle?
I am a fan of the circular needle, but this is not important in your adventure to start knitting. Over time you will develop a preference for certain needles. As someone just starting out you should look for a pair of 9" straight needles. Straight needles come in longer sizes, but for a scarf you won't need the extra space of a longer needle and shorter needles are easier to wield.
What material should the needles be made out of?
Again over time you will develop a personal preference depending on how tight or loose you knit. But when you are just starting out give the bamboo a try. They are light, and smooth, strong, warm to the touch, and flexible. Bamboo is also renewable resource. (Did you know bamboo can grow up to 12 inches in one day!)
Once you fall in love with a yarn look for an appropriate sized pair of 9" bamboo straight needles and you will be ready for action. Just like buying yarn ask questions and let the employees know what you are looking for.
Clover 9" Straight Needles
Knit Picks Harmony Straight Needles
Wiki How: How to Choose Knitting Needles
Blue Betty: Bamboo, Wood, Steal or Plastic