This is the 877th most frequent Russian word.
внимательно
Attentively.
adverb, modifying the verb 'listen' to show the manner of listening
Слушайте внимательно, это важно.
Listen carefully, this is important.
adverb, indicating the manner of observation
Она всегда смотрит на людей внимательно, когда они о чём-то говорят.
She always looks at people attentively when they talk about something.
adverb, describing how the action of reading was performed