Amazon RDS is pure MySQL, accessible by your app the same way as any other MySQL database; the web services interface to RDS is purely for creation, deletion, and modification of the DB instances, not the DB data. From their FAQ:
Q: How do I access my running DB
Instance?
Once your DB Instance is available,
you can retrieve its
endpoint via the DescribeDBInstance
API. Using this endpoint you can
construct the connection string
required to connect directly with your
DB Instance using your favorite
database tool or programming language.
In order to allow network requests to
your running DB Instance, you will
need to authorize access. For a
detailed explanation of how to
construct your connection string and
get started, please refer to our
Getting Started Guide.
This is the part of the Getting Started Guide you need -- it explains how to get the hostname of your new instance so you can connect to it, authorize the instance for access from the client, and then connect using the MySQL command-line client (as an example):
$ rds-describe-db-instances --headers
$ rds-authorize-db-security-group-ingress default --cidr-ip 192.0.2.0/30 --headers
$ mysql -h myinstance.crwjauxgijdf.us-east-1.rds.amazonaws.com -P 3306 -u mymasteruser -p