Quick search for an object in an array

The task is to quickly find an object in the array.

There is an array containing data about users. During the course of the program, the data of individual users will change. What is the most efficient way to search for a user in an array?

I've read about hash functions and hash tables, but I don't fully understand how I need to use them. I should create a dictionary like:

{'name of user': index}

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