What is my iPhone s identification

I have been given this Iphone that I believe was hardly used if atall,but think its been sitting unused for a good while,I see phones that look the same but are called generation 4,or 5,or 6, or 6s etc I am useless at these things but did notice capacity said 6.2 GB and I know they go lot higher, so is mine really old or am I seeing it wrong ? not sure its ever actualy been used ,still has back plastic on it but seems to have everything far as menu goes though some items appear to have never been set up . The only thing I can see tha may help is that it sayse it is ios7.1.1.so is this a 4, or 5, or worse lol. anyone with a better clue than me would be helpful, thank you