Before executing below step login as root to your OpenBSD
1. make sure PKG_PATH is correctly pointing to mirror containing openbsd package.
check it with set command on shell and search for PKG_PATH
PKG_PATH=http://ftp.jaist.ac.jp/pub/OpenBSD/6.1/packages/amd64
if not set or not exist execute command below
export PKG_PATH=http://ftp.jaist.ac.jp/pub/OpenBSD/6.1/packages/amd64
2. add postgresql server package
pkg_add postgresql-server
3. connect to postgresql user
su – _postgresql
4. create directory to hold data
mkdir /var/postgresql/data/
5. init database and set password with md5 auth
initdb -D /var/postgresql/data -U postgres -A md5 -W
6. to start postgresql server
/etc/rc.d/postgresql start
7. configure for auto start at system boot by adding postgresql to pkg_scripts on /etc/rc.conf.local
if /etc/rc.conf.local is not exist then create it and add as follow
pkg_scripts=postgresql
8. install pgadmin3 and postgresql-client if needed
pkg_add pgadmin3 postgresql-client
9. execute pgadmin3 under xwindows and connect to postgresql using user postgres and password set before
Good luck …