Hello world example

$ juju bootstrap aws ctrl1
$ juju deploy mysql
$ juju offer mysql:db hosted-mysql

$ juju bootstrap aws ctrl2
$ juju deploy mediawiki
$ juju expose mediawiki
$ juju relate mediawiki:db ctrl1:admin/default.hosted-mysql

On the offering model, see what offers are and who is connected:

$ juju switch ctrl1
$ juju offers

You can also use permissions. People with consume permission can access an offer without having other rights to the model. On ctrl1:

$ juju grant fred consume admin/default.hosted-mysql

Now, if "fred" has login access to ctrl1, he can consume that offer.
You can also run these (see their --help)

$ juju find-endpoints
$ juju show-endpoints