We indeed cannot and never have seen atoms. As stated in
the text, it is, in fact, impossible to see atoms, as light
cannot bounce off of a single atom, which is necessary for us
to see them. Thus, we will never be able to see atoms.

Nevertheless, we can study things that we cannot see. We
know a lot about gravity, for example, even though we cannot
see gravity. Nevertheless, we know so much about it that we
can use our understanding of gravity to describe our solar
system and even the structure of the universe in general.

In the same way, we can study atomic structure even though we
cannot see atoms. For example, Ernest Rutherford did a
famous experiment in which he determined that the atom was
composed of a positively-charged nucleus surrounded by
electrons, even though he could not see the atom, the
nucleus, or the electrons.