Welcome to the forums
Google Base is pretty easy to set up. First you'll need to create an account with Google. This url is a good starting point:
http://www.google.com/base/help/sellongoogle.html
Google Base works like this:
Create an account with Google Base. This will also give you the FTP login info you'll need to upload your feed file.
Create an upload profile in Google Base that specifies the file format, what type of products you're uploading, etc.
Use the AbleCommerce feed builder to generate the feed file and upload it to Google.
Google will then notify you if the feed is ok. This usually takes 1-2 hours, maybe longer if you're a new account.
Some things to keep in mind:
Able's feed builder uses the Summary field on each product description uploaded to Google.
HTML tags are not allowed in the product descriptions sent to Google. This will (usually) get your product rejected by Google.
Out-of-stock i.e. 0 inventory items will not be acceptable by Google.
The other feed builders work in similar fashion. Create an account. Upload the file. Wait for success or error. Fund the account. Sell!
The nice thing is Google is still free.
Here are a few articles I've written a while back on my experiences with online marketing:
viewtopic.php?f=47&t=6592
viewtopic.php?f=42&t=6749&p=27826