So, to get started you need to get the base OS installed using the instructions from the official docs .
$ pkg update
$ pkg install bsdtar wget proot tergent tmux openssh
Tmux is a multiplexer that lets you run multiple persistent windows and sessions on a single terminal. I had trouble getting it working in the Arch proot, so a workaround is configuring tmux from your host Termux and then creating a tmux session and starting the chroot from there. For more information on using tmux read this article, and to learn how to customize the appearance and behaviors more try this one as well as looking at the tmux-plugins Github organization for community-built add-ons.
$ termux-setup-storage