We use the Present Continuous for what someone has arranged to do in future. For example
I am watching a movie in the evening.
In the above sentence the arrangement of watching a movie has been arranged in advance, so the action can be expressed in Present Continuous.

Some more examples are
We are having a party tomorrow. (Party is arranged for tomorrow)
She is coming to visit me this Sunday. (Visit is planned for this Sunday)
They are going for vacation this summer. (Vacation is decided this Summer)
They are buying a house this Diwali. (Purchase is finalized for this Diwali)
Salman Khan’s movie is releasing this month. (Release of the movie is pre-set)