While many people use nothing by dry yeast and have good results, if you do choose to go liquid either with Wyeast or White Labs a starter is really going to help.
A basic rule of thumb for your basic starter is 1 cup of light or extra light dry malt extract per liter of water. You can use Mr Malty Pitching Rate Calculator
to determine what size starter you need, but most of the time you will be able to get by with a 1-2L starter.
Making the starter is easy. Bring your water to a boil and then add the DME. Boil for 10-20 minutes. Then bring your wort to room temp by a cold water or ice bath. Use a sanitized flask, mason jar, etc to put the wort in and pitch the yeast. Cover with a sanitized piece of aluminum foil. Then, give it somewhere around 12-36 hours to be ready to pitch into your wort. It helps if you can keep it aerated, so regularly give it a good swirl.
Some people pitch the whole starter, some decant the liquid and pitch just the slurry. A lot of different options but that should give you a general idea for your first one.