How to calculate hours/month usage on Amazon RDS and Pricing?

I never used Amazon EC2 or RDS Service. I am trying to calculate my cost using http://calculator.s3.amazonaws.com/calc5.html

I searched a little but could locate answers to some basic things. Can you help me out with this:

1. What does DB Instance means? 1 Database = 1 开发者_开发技巧Instance or 1 Connection = 1 Instance
2. How to calculate hours/month usage? It should depend on the transfer rates or processing time. Is there a way I can get rough Idea about it?
3. What if I already have my DB Ready and want to upload it directly (it would be few GBs) then how will it be calculated.

I am new to amazon EC2 and searched stackoverflow and serverfault before posting this question. Got some idea but not specific what I am looking for. Can someone help me out here?

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1. In general, one database = one instance. You spin up instances, and do what you like with them. Definitely possible to have more connections to it.

2. Hours per month is just that. How many hours per month you have the instance active. If you plan to have the instance active 24/7, you may find more cost effective alternatives with other cloud providers. If you run it less often than that, you save money when it's not active. It's billed hourly to your account at the rate specified.

3. Upload data is counted at the standard transfer rates. A few GBs doesn't cost much, but you will be paying for the service starting the moment you spin up the instance.