Android Question Need to make alert/notification even with program off, like in Whatsapp and Messenger

Dear All.
hope to make my program start automatically with phone startup, and
receive notification or alerts from server

" Like in Whatsapp , Messenger, Skype, and many other program "

i.e. the Whatsapp sure work in hidden, and receive alert/notifications for new message, and so you can run the program in full screen or not.

Also, if the program have schedule of timing to run also automatic according for these times

Thanks in advance

Best regards