The LFS book covers setting up networking by connecting to a LAN with a static IP address. There are other methods used to obtain an IP address and connect to a LAN and other networks (such as the internet). The most popular method is DHCP.
DHCP stands for Dynamic Host Configuration Protocol. It is a protocol used by many sites to automatically provide information such as IP addresses, subnet masks and routing information to computers. If your network uses DHCP, you will need a DHCP client in order to connect to it.
In order to use DHCP, you will need a DHCP client, dhcpcd. You may also be wanting to connect to the internet wirelessly. In order to do that, you should first configure the kernel to support that, the instructions for that being at https://www.linuxfromscratch.org/blfs/view/svn/basicnet/wireless-kernel.html. After that, you will need a tool to connect to the internet, suitable ones being iw, Wireless Tools, and wpa_supplicant. You will only need one of those, whichever one is up to you.