Assuming you have a fresh FreeBSD (or a jail) installed, and you are logged in as root, download the latest version of BIP148 enabled bitcoin sources from here as .tar.gz file and untar it. As of writing it is v0.14.1-uasfsegwit0.3.tar.gz.
fetch https://github.com/UASF/bitcoin/archive/v0.14.1-uasfsegwit0.3.tar.gz tar xzvf v0.14.1-uasfsegwit0.3.tar.gz cd bitcoin-0.14.1-uasfsegwit0.3
Next the documentation in ./doc/build-unix.md tells us which packages we have to install to compile bitcoin. Let's install them:
pkg install autoconf automake libtool pkgconf pkg install boost-libs openssl libevent pkg install gmake
And now compile and install bitcoind:
./autogen.sh ./configure --without-gui --without-miniupnpc --disable-wallet gmake gmake install
Now start bitcoind
Make sure your server is reachable over port 8333.
To check your node go to bitnode and enter the ip address of your node. You should get a result similar to this: