Answer:
Federalism provides a way for different groups of people in different parts of the country to live together
Federal systems have at least two levels of government, the central level and a second level that includes territorial entities into which the country is divided, e.g. regions, states, provinces.
Federalism provides ways by which these different groups share power over common interests, but it also provides for these groups to have a level of autonomy vis-à-vis central state institutions
Federations are protected by a constitution regarding ways in which power is shared in central state institutions, but also regarding the powers and responsibilities of both the central state and provinces, states or regions.
But federalism is not a panacea. There are specific challenges that federalism alone cannot resolve, e.g. how to protect minorities, or the fact that federalism can be expensive as you need to build institutions not only and the central, but also at the region, state, provincial level. Sometimes the different levels have difficulties coordinating policies or policy responses, such as to pandemics or natural disasters.