Please correct me if i'm wrong. As far as i know, when we use vpn service, our datas are only encrypted from us to vpn server. After leaving the server to intended recipient, our data is decrypted and interceptable by any party who is spying us.
Yes. This is essentially correct. A notable example would be an embassy which used tor - and the person running the tor exit node snooping on the traffic.
Note that the example is old - from 2006-2007. At that time clear text protocols was the norm, and only banks and similar sites bothered with https.
Today, the norm is https and encrypted protocols for almost everything. Even news websites uses https. Heck, my personal blog uses https - because it's essentially free. Let's encrypt was a major driver here, as they made certificates free for all.
How to prevent our data from being intercepted or viewed until it reaches the destination? Does using Signal messaging app make our data encrypted from point to point?
Signal is one example of end to end encrypted protocol, where data is unreadable by anyone in transit. The provider or anyone in the path is unable to read the messages.
With for instance Facebook's Messenger service, the data is encrypted between you and the server, and between the server and other clients, so a VPN server or tor exit node can't read your data - but Facebook can.
End to end-encryption means that the data is unreadable to anyone in transit. With e-mail this may be achieved with PGP or S/Mime. Otherwise, e-mails will at most be encrypted between user and servers, but readable in clear on the e-mail provider servers.