Installing termux is easy, just goto the Google play store and install.
Once installed, type the following into termux
pkg install curl
pkg install zsh
pkg install git
install oh my zsh (from ohmyz.sh)
sh -c "$(curl -fsSL https://raw.github.com/ohmyzsh/ohmyzsh/master/tools/install.sh)"
next, change your default shell
type in zsh when prompted.
next, exit from termux and re-open.
welcome to zsh with oh my zsh!
next, lets set up some things – powerline fonts and agnoster theme
# go to home dir
# clone this repository - git clone https://github.com/adi1090x/termux-style
# change to termux-style dir
# to install it, run
# And Follow the steps, it'll be installed on your system.
to select the agnoster theme, edit the ~/.zshrc file and change the line for ZSH_THEME to agnoster