With «Send now», you instantly send to all your bot users messages you build in «send now».
You can send message with text cards, image cards, galleries and plugins. You can’t send Forms because they can break current users sessions, so if you want to get forms filled, send a message with a button connected to the existing form in structure.
All your bot subscribers will instantly get this broadcasting message. If you want to delay your message — use «Sent on schedule». If you want to send repeated content, for example, daily digest of your news from RSS feed, use «Recurrent events».