Install MODX locally (1st time)

Designer here with very little experience of phpMyAdmin and databases trying to install MODX locally. It's actually a MODX 3 nightly so hopefully thats not my issue. I realise it's not released yet.Normally my host and MODX Cloud handles the setup for me so I'm a bit confused about the steps here.

What I have:
Macbook with MAMP installed and running.
MODX Setup screen at Connection Information screen (see attached modx-install.png)

Steps

1. Created a new database in phpMyAdmin with the name of modx3
2. Visit setup page as illustrated in the attachment
3. Hit "test database server connection" and I get the success message
4. Try the character sets and collations of: UTF8 and UTF8_general_ci
5. Hit "Create or test selection..."

Result: Checking database: MODX could not create your database. Please manually create your database and then try again.

I'm confused about this part as I have created the database manually in phpMyAdmin.
The only thing I can think of is there are no tables created in the database by me.
Do I need to create those manually myself or is that not the issue?

Thanks

Access denied for user 'root'@'localhost' (using password: NO)

Try using "root" as your password.

Thanks Labr
Was under the impression from some forum research that I could leave the password field blank. Obviously not.

Yes, a default MAMP installation has the database username "root" and password "root"; you need both. The MODx installer script can create the database for you. You should make sure that the database is set with a charset of utf8, and collation of utf8-general-ci.

Thanks Susan.
Got it working and installed once I figured out my original password.
On a side note, where can I download and test MODX 3? The nightly for V3 which I downloaded is an older June 2013 version and doesn't have some of the new features I've seen in dev on Git. I realise it's not yet ready for release but wanted to have a look.

I've gotten it from here https://github.com/rthrash/revolution

You have to build it yourself using the scripts in the _build directory before you can install, and the last time I tried it the poor thing was definitely cranky - no menu items in the menu bar. That was a few days ago, so I don't know what its status is at the moment.