Cocoa beans have numerous similarities to coffee beans, with some important differences in processes. They are both fermented (fermented cocoa almost looks already roasted), roasted and ground for use. Cocoa beans come in three primary species, Criollo, Forastero and Trinitario, but there are hundreds of sub-varieties for each. Very loosely, Criollo is analogous to Arabica coffee in that it is the cream of the crop and has the most delicate and complex array of flavors. But in many cases, this can also mean a very mild chocolate.
The Forastero can be compared to Robusta coffee in its disease resistance and higher production, but that is where the comparison ends. Where robusta is just horrid 99% of the time, Forastero is not like that. It has a strong full cocoa flavor, but depending on the grade and preparation, can be rather one dimensional. Well prepared Forastero is what most of us are used to eating in chocolate.
Finally, Trinitario is a hybrid of the two, and can have various characters of both parents. Often a Trinitario bean is spoken of as having a strong or weak Criollo influence.
Unless specifically labeled, the cocoa beans or nibs you have purchased in their raw form. They are best kept in a cool, dry, sealed location. Like this, they should remain "fresh" 6 months to a year. I don't recommend refrigeration or freezing as it is easy to trap moisture which is not good for cocoa beans.
I recommend leaving them in their raw form until you are ready to use them. Roasted beans go stale quicker than raw beans, usually with a shelf life of around a month.
Roasted vs Raw
I know there is a lot of information out there about the health benefits of chocolate, and I know some people like to eat cocoa in it's raw form for "maximum" health benefits. Personally, I do not recommend eating ANY cocoa raw. All commercial cocoa beans have been fermented by various yeasts and micro organisms, and are often open air dried. In addition, e.coli and Salmonella can be present on the surface of the husk. Proper roasting completely kills any potential surface contamination that may be present, makes them safe to eat and develops the flavors associated with chocolate. And proper, delicate roasting does not significantly reduce the health benefits of cocoa - after all, the benefits were originally found in finished chocolate, not raw cocoa beans. Keep that in mind.
There is even some debate as to whether the nutrients and various flavonoids are even nutritionally "available" in the raw form since roasting alters the physical structure of the cocoa bean and makes it easier to grind. If you do want to eat cocoa beans whole as a snack, go right ahead - just roast them first. And if you really don't want to roast them, please peel them.
You can see the wide variety of appearances the cocoa beans can take and how fermentation can affect that appearance.