This is the 10933rd most frequent Russian word.
выслав
"Выслав" means "having sent out" or "after sending out."
The word 'выслав' is used as a past active participle here, referring to the action of sending carried out by the subject before receiving the confirmation.
Выслав документы, он получил подтверждение.
Having sent the documents, he received a confirmation.
'Выслав' indicates the action of sending the letter, which precedes the decision to wait for the response, showing sequence in actions.
Он выслав письмо, решил подождать ответа.
He, having sent the letter, decided to wait for a response.
Here 'выслав' shows that Masha sent the parcel before calling her friend, emphasizing the completed nature of the first action.