See this page for more details on how to install VirtualBox: https://www.virtualbox.org/wiki/Downloads/

• Check if any update:
  $ sudo apt update
  
• Install VirtualBox:
  $ sudo apt install virtualbox virtualbox-ext-pack
  
• Check VirtualBox packages:
  $ apt list --installed | grep virtualbox virtualbox/bionic-updates,now 5.2.42-dfsg-0~ubuntu1.18.04.1 amd64 [installed] virtualbox-dkms/bionic-updates,now 5.2.42-dfsg-0~ubuntu1.18.04.1 all [installed,automatic] virtualbox-ext-pack/bionic-updates,now 5.2.42-1~ubuntu1.18.04.1 all [installed] virtualbox-guest-dkms/bionic-updates,now 5.2.42-dfsg-0~ubuntu1.18.04.1 all [installed] virtualbox-guest-utils/bionic-updates,now 5.2.42-dfsg-0~ubuntu1.18.04.1 amd64 [installed] virtualbox-guest-x11/bionic-updates,now 5.2.42-dfsg-0~ubuntu1.18.04.1 amd64 [installed] virtualbox-qt/bionic-updates,now 5.2.42-dfsg-0~ubuntu1.18.04.1 amd64 [installed,automatic]