You might wanna visit your local bike shop (lbs).
You'll probably need them to a. install headset, b. install bb and cranks. Unless you wanna buy the tools to do it yourself. Which cost as much as 3-4 visits to the LBS.
I dont know your mechanical expertise level, who may know it all already and just need the bb tip. But i thought somebody ought to advise visiting the LBS. Seems like everyone assumes folks have all the tools and plenty bike building experience. I doubt this is true in most cases. Better to pay someone 20 bucks and make a friend than diy and booger up a frame or pricey component, then STILL have to visit the LBS.
Your frame has either a 68mm or 73mm shell (see surly specs) and needs a spindle somewhere between 108-118mm depending on crank. If its a sq taper you probably need ~113 ish. If isis still probably 113. Isis only come in 108 113 and 118 (i think). Sq taper come in 107 110 113 etc, more choices.