1.As means in the role of.  

Pattern 1: verb + as + noun
She is a trained teacher, but she works as a secretary in our office. 

Typical verbs used before as:
act, serve, substitute, volunteer, work  

Pattern 2: verb + noun + as + noun

We have selected you as the captain of the team.        

Typical verbs:
choose, elect, nominate, pick, select, use       

2.Expression                

 as for me—regarding me
They all went to the movies; as for me, I stayed home.  

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