Install the Vivado toolchain. You can download Vivado using this link. The 2017.3 or newer version of Vivado is recommended.
Get all required submodules:

git submodule update --init --recursive

Get all required packages:

apt-get install build-essential bzip2 python3 python3-dev python3-pip
./install.sh

Build bitstream following these steps:

source ./init
source ${PATH_TO_VIVADO_TOOLCHAIN}/settings64.sh
./make.py --board=arty --build --with_mmcm --with_i2s --with_ethernet

Connect your board using the serial port then,
load bitstream following these steps:

source ./init
./make.py --board=arty --load