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The real computer is called the host. The Sandbox creates one or two Virtual Machines (VM) that run under the host operating system.
The Sandbox is distributed as a *.ova file. This is an open standard form of zip file that contains both the machine configuration and the disk image. It can be loaded into VirtualBox (or VMWare for that matter) to create the virtual machine. Once the VM directory is created, it contains configuration files that point to specific local machine values (the full path to files for example). A VM is not portable, but a *.ova file created from a VM directory can be moved.
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NAT is an automatic service that is part of VirtualBox and requires no configuration. However, a Host-Only network has to be set up before any VM can use it. In the VirtualBox management console (that lists the installed virtual machines). Click File - Preferences - Network. Select the Host-only Networks tab. If no network is listed, click the Add 
button to create one. It will be called "VirtualBox Host-Only Ethernet Adapter" and when you create it you have to let your real laptop operating system add a new device. If you double click the now listed adapter, you can set its IPv4 Address to 192.168.137.1 and the Network mask to 255.255.255.0. It does not need a DHCP server because static addresses are configured in the VMs.
The Sandbox VM comes configured with two LAN adapters.You can configure them when you import the VM from the original distribution file image. The distribution format (the *.ova file that you install to get the Sandbox VM) sort of knows that one of them is supposed to connect to the Host-Only adapter and one is going to use the NAT service, but that depends on VirtualBox mapping information from what is supposed to be an open file format to two rather specific VirtualBox features. The first time you do this, you need to check that the two LAN adapters actually get connected correctly. For example, if you did not follow the previous instructions and did not create the Host-Only adapter on the host computer, then there would be no Host-Only adapter to connect the Sandbox VM to, and then one of the two LAN adapters is left in an unclear state. Virtual hardware such as LAN adapters can be configured at the start of the *.ova file import process, or you can reconfigure them in the VirtualBox management console before you start the VM. Select the Sandbox VM and click Settings - Network. Adapter 1 should be "Attached to" Host-only Adapter and Adapter 2 should be attached to NAT.
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