This is a redis database error, you will need to look in config.json for your database configuration.
Redis host is 127.0.0.1 on port 6379. If you've added a password in redis.conf within /etc/redis/ then you'll need to add it here too. If not, you can leave it blank, but that's not very secure. Database is usually set to 0, but this isn't really very important in the grand scheme of setting up a new forum.
URL should be set to your servers IP Address:4567 (i think, mine is just the URL of the forum, then nginx handles the reverse proxy)
I've not seen or used the web installer so I don't know how it works, I probably should test it to get some experience so I can try and support it. But via SSH, you should be able to do it with the following commands.
Once you have the files in a folder.
./nodebb setup (here is where you specify an admin account etc)
./nodebb dev will give you a stack trace of everything that happens when nodebb starts, including any errors it encounters such as missing dependencies.