Prepositions – As

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.