(I assume you meant 2.16.x.)
For Gitiles, there's not much to do after installing the plugin, really. By default, without configuration, it "should just work". So, please provide some more information:
Do you see the plugin listed in the list of plugins?
(Assuming you have the permissions to list the, go to menu Browse -> Plugins, or navigate to '/admin/plugins' in your browser, relative from the base-path of your Gerrit installation.)
If yes, what do you see on the repository listing page in the "Repository Browser" column? (menu Browse -> Repositories, or navigate to '/admin/repos' relative from the base-path of your Gerrit installation.) It should look like this:

If no, what do you see in the Gerrit server side logs? It should list the gitiles plugin attempt to load, e.g. the following is indicated on my installation where it works fine:
[...]
[main] INFO com.google.gerrit.server.config.PluginConfigFactory : No /var/lib/gerrit/site/etc/gitiles.config; assuming defaults
[...]
[main] INFO com.google.gerrit.server.plugins.PluginLoader : Loaded plugin gitiles, version 623105f
[...]
[main] INFO com.googlesource.gerrit.plugins.gitiles.HttpModule : No /var/lib/gerrit/site/etc/gitiles.config; assuming defaults
[...]
HTH