1) First, you'll need to run as the postgres user:
su postgres

if you don't already have  the plpgsql language installed, install it:
psql -d template1 -f plpgsql.sql

2) Run
psql -d template1 -f 1CreateDatabase.sql

3) Create a mojoportal user:
createuser --pwprompt --no-adduser --no-createdb mojo

4) Ensure that mojo can connect through tcpip:

If your database server and webserver are on the same machine, add these 2 lines to the the top of /var/lib/pgsql/data/pg_hba.conf to create the least privileged settings for mojo to connect from the local machine.

host mojoportal mojo ::1/128 password
host mojoportal mojo 127.0.0.1 255.255.255.255 password

If your database server and webserver are on different machines, make sure the firewall on the database server machine is open to tcp traffic on port 5432 from the webserver and see the PostgreSQL documentation for details on setting listen_addresses in postgresql.conf and setting up pg_hba.conf to allow access from remote hosts.

If you want to make the postgresql server listen on all its ip addresses, in /var/lib/pgsql/data/postgresql.conf:
listen_addresses = '*'
by default it is only listening on the loopback address 127.0.0.1
you can also specify an ip address range if you don't want it to listen on all its addresses, but often there is only 1 address anyway.

5) As root, restart posgresql.
/etc/init.d/postgresql restart

6) Then just make sure that you change the password in the web.config or user.config
to the password you specified when you created the mojo user.

Navigate to yoursiteroot/Setup/Default.aspx

If you have any trouble, please post in the forums and specify your  versions of OS, db, mono and mojoPortal