A while ago I created a serie of topics on SSH and VNC for Manjaro and the last one specifically for Raspberry Pi.
- [root tip] Set up your own SSH service
- [root tip] TigerVNC over SSH
- [root tip] Install Raspberry Pi - VNC over SSH
As @Nachlese said - you need to enable the service to be able use it after reboots.
Without knowledge on excatly which Manjaro you installed on your PI - I know that at least the miniminal edition comes with ssh enabled since it is designed to be headless and thus only accessible using ssh.