For a new user the likely easiest route is to use sysinstall.
As root:
#sysinstall
select the following (each line represents an option from menu)
Configure
Networking
Interfaces
You can skip ipv6 setup, then select DHCP.
That should configure your ethernet.
If there are multiple listings for ethernet cards (probably not in a laptop) the way to tell which one to use is from a command prompt type "ifconfig" and look for a line that looks like this:
media: Ethernet autoselect (1000baseT <full-duplex>)
That interface has a working cable attached to it and that is the one you want to use.
To see what sysinstall did:
cat /etc/rc.conf
Later if you wanted to switch to a static IP you would edit your /etc/rc.conf to look like:
defaultrouter="###.###.###.###"
ifconfig_em0="inet ###.###.###.### netmask 255.255.255.0"
Where ### represent IPs. If you are doing this home there is a good chance your router/gateway is 192.168.1.1 and you could assign to your machine something like 192.168.1.100.
If you have other devices and you can check what IPs they are using try to assign your FreeBSD machine an IP away from those. For example if your router is assigning IPs above 100, then setup your machine to IP of 10.