how to send message to some one contact?

[codenong]

Thanks for your work.

My application scenario is as follows: another app sends a message to the bot, and the bot forwards this message to certain contacts. Currently, there are two issues:

How can the other app send messages to the bot? (I am considering reading a file or database periodically.)
How can the bot proactively send messages to contacts?

where I can find the document or example?