Question: After generating a tags file with `exuberant-ctags` I can jump from a function call to its declaration with `<C-]>` which is pretty convenient.

My question is how to do it in the other way? When my cursor is on the definition of a function, how can I go to the lines where the function is called?

When I look to the file generated by ctags I only see informations related to the location of the definition and not of the calls, does it means that I can't do that, that Vim as a clever workaround or that I need to use something else than `exuberant-ctags`?

Answer: 
You can't jump to function calls with `ctags`. For C/C++ and Java there is [`cscope`](http://cscope.sourceforge.net/), and it integrates nicely with Vim (see [`:help cscope`](http://vimhelp.appspot.com/if_cscop.txt.html)). For other languages you might be able to find a tool that generates / exports `cscope`-compatible databases (f.i. [`hscope`](https://github.com/bosu/hscope) for Haskell, and [`starscope`](https://github.com/eapache/starscope/) for Ruby, Go, and JavaScript). You can also use `cscope` with [GNU global](http://www.gnu.org/software/global/) databases, by pointing `cscopeprg` to `gtags-cscope`.

On a side note: if you aren't put off by occasionally puzzling use of [Engrish](https://en.wikipedia.org/wiki/Engrish), ;) you probably also want to use [universal-ctags](https://github.com/universal-ctags/ctags) instead of `exuberant-ctags`. The latter hasn't been updated in years. The former is an actively maintained fork.
You can't do that with ctags.

Try a beefier alternative like [cscope](http://cscope.sourceforge.net/) (which even has its own help section: `:help cscope`) or [global](http://www.gnu.org/software/global/).