として marks the role or capacity in which the subject does something or is evaluated. It answers 'in what capacity?' or 'as what?'. The noun before として is not marked by は, が, or を; the whole phrase acts as an adverbial. It is common in both speech and writing, though a more formal nuance exists when used in official contexts.

You can use として with personal roles (e.g., 学生, 親), professional roles (e.g., 医者, 先生), or abstract categories (e.g., 趣味, 記念). It often appears with verbs like 働く (work as), 参加する (participate as), or 考える (think of as). Note that として does not mean 'like' or 'similar to'—it means actual role, not comparison.

When the role is the basis of an opinion, you can also use としては (as for, from the standpoint of), but として alone is plain 'as'.