Getting geared up
If at all possible wait until you have a lesson and allow your instructor to recommend a rod that is well suited to you. Your hand size, physique and overall muscular skeletal reflex are all relevant. Later as you gain proficiency you can adapt your cast to a new rod regardless of its action, however not so much at this stage of the game.
Nothing worse than learning to cast the fly with something that "just plain" doesn't suit you, or was really a good deal but useless for
the task at hand.

Why lessons?
Okay, here goes - no holds barred. 
Two to three hours of private instruction will set you up with a solid foundation or base of repeatable drills. 
It is these drills that will allow you to improve every time you pick up a fly rod to cast as opposed to flailing in frustration outing after outing as a result of not having any points of reference for the creation of a series of required mechanical steps in the formation of your cast. 
All of which by the way are elemental to the success you are pursuing so avidly. - So - 
3 hours and 40 feet or more every cast (improving at each outing) and knowing 
how to repair the cast that failed!
Multiple outings of lost flies, knotted leaders and fish that are always out of reach? And no idea what or how to correct whats not working.

Sort of like learning to ski or board, by going with well intentioned friends who really just want to giddy up and go. Takes longer and is a painful process.

Accelerated from a fixed point (forward) to another fixed or stop point (Rear), there is a rapid transfer of energy which throws the line out away from the rod- the pull of the line flexes the rod and loading is achieved.

About rods
Fly-rods are designed to flex (bend) as the combined weight (of the feet/inches/cms) of the Fly-line which extends beyond the tip of the rod and is moving away from the tip either in a forward (forward cast) or rearward (back cast). Much like the building and storing of energy in the limbs of a bow as an archer pulls the strings and flexes the limbs, there is a building and storing of energy within the rod as it flexes in response to the extension of the line.
More on this later.
Rods are described generally with the following terminology:
   SLOW  - A soft or easily flexed (loaded) rod with a given amount of line in play
 MEDIUM  - A firmer or stiffer rod than the slow rod, requiring either more energy or more line in play to flex (bend or load) the rod.
            FAST  - A very stiff rod requiring considerably more energy and or line or both to achieve effective flex (bend or load) of the rod.

    There are numerous variations on the basic three rods types described above, do not spend a minute at this stage of the game worrying about those.