The simplest way is to set the virtual machine to use bridged networking, it will get an IP address on your network; this IP address should then be accessible from your host machine.
From Chapter 6 of VirtualBox's manual:
With bridged networking, VirtualBox uses a device driver on your host system that filters data from your physical network adapter. This driver is therefore called a "net filter" driver. This allows VirtualBox to intercept data from the physical network and inject data into it, effectively creating a new network interface in software. When a guest is using such a new software interface, it looks to the host system as though the guest were physically connected to the interface using a network cable: the host can send data to the guest through that interface and receive data from it. This means that you can set up routing or bridging between the guest and the rest of your network.
It is also possible to use the NAT networking mode, but it will require tinkering with port forwards (not worth the trouble, in my opinion).