How can I implement a class which can be constructed with an input iterator?

How can I implement a class which can be constructed with an input iterator?

The std::vector class has a convenient constructor which allows any input
iterator for its parameter. I would like to implement a similar pattern in
my own class, because the class needs to take in some collection when
instantiated, but I would like to have the iterator over that collection
for encapsulation purposes. One way that I thought of to do this is
template-ing the whole class with the input iterator type, but that can't
be what STL does, because vector is clearly only templated with the type
being iterated over. Of course, one option is a templated generator
function, but I'd really like to know how its done by compilers that
implement STL - somehow, the InputIterator type is a typename specific
only to the constructor, even if constructors can't be templated.
(Yes, I have tried to look at vector.tpp but I could not understand it).