The standard system is 4d6-drop 1, which means you roll four six-sided dice (4d6), take the three highest rolls, and add them together. It's best to have someone else from the group witness your rolls so that no one thinks you cheated. The standard method is rolling for stats.
Either way, it's ultimately up to the DM, and he or she will likely have special rules in regards to finding your stats. First, you should establish if your DM is going by a point-buy system or rolling. Stats are the lifeblood of your character. Personally, I think a Fighter is the best class for a beginner. Rogues don't deal with magic, but have a greater deal of skills to deal with, and are often very dependent on role-playing ability. Fighting classes (Fighter, Barbarian, or Monk) are generally easier for beginners because you don't have to worry about the magic system for them.
