Advocacy can be done in a lot of different ways, but also on a lot of different levels. Within each of these levels, you target different people, such as community leaders or the Mayor (local), Members of Parliament and policy makers (national), international companies, organizations, or delegates at a UN meeting (international).
When advocacy is done on a local level, it often targets and is driven by the local community. Local advocacy tries to positively affect the local communities directly, by involving them in the campaign and cooperating with them to ask for change!
We speak of national advocacy when it is done at a national level. National advocacy can target a change where the entire country benefits from, or also a change at the state/province level.
International advocacy targets a worldwide audience and national policymakers who are involved in international processes and often wants to bring change in international agreements about a specific issue.
Surf the internet and look for examples of national or international advocacy campaigns. Were they successful? Why (not)? Did they bring about change?