The process is quite simple. Apply directly to the company, go for an interview, do psychometric testing, do a medical and then you're hired.
I was asked to give examples about demonstrating things like teamwork, safety, how my values align with the company etc. I was also asked what my career goals/aspirations are and where I saw myself in 5-10 years time.
Alcoa doesn't ask technical questions, so don't stress about that. Instead, focus on making sure you can use the STAR method to give practical examples of you demonstrating the company values and the core behaviours that companies typically look for eg. teamwork