In answer to the question about what are differences we need to separate the Philosophical basis of the ideology from how they act as a nation state.
Fascism begins as an ideology that appeals to conservatives, a sort of tribal thing where the treasured traditions and economic stability of a core group of "real citizens" are under threat from some other internal group, usually liberals, immigrants, ethnic groups and intellectuals.
Communism began as a liberal reaction to concentration of wealth and power among the political elite and the owners of the means of production, In our case you could call them the 1%, and a total inability to pry democratic reforms from a monolithic power structure.
These two ideologies are polar opposites in their origins, one seeks to preserve power among the establishment and the other seeks to tear down the establishment.
The thing to remember is that both ideologies seek to create a nation state that runs counter to human nature and both use blind nationalism as a way to bind the populace together and maintain power. This is the aspect that many look at and find there is no difference. Both end up having a powerful elite in charge, both are authoritarian, both end up being very corrupt and neither trusts democracy to produce the ends they wish.
In the end both are authoritarian because force and coercion must be used to maintain their nation against people naturally just wanting to be left alone to pursue their lives but even here the people in charge are different.
Under a fascist system there is a large degree of freedom for those deemed worthy of power, the owners of the means of production and their close partners in the government and the military brass. The state is the mechanism of expanding their personal wealth.
Under communism, Soviet communism in this case, all the wealth is owned by the state and the elite get to use it to further themselves but do not actually own anything, all their power is purely political. The state is the mechanism to further itself and individual power is allowed only as long as it serves the state.
