To accept payments in Nigeria, you can use Moneybookers. I just checked their website and they offer services in Nigeria. For detailed withdrawal methods you should check when you create an account. It's free.
To find freelance jobs, use websites like:
http://www.getafreelancer.com
http://www.scriptlance.com
http://www.eufreelance.com
...
Every one of them has Moneybookers as withdrawal option.
Also to find more freelance jobs, you should use forums like this one. Everything else is a waste of time. DON'T fall for processing e-mails scam. Those websites will only collect your payment and then will offer you to promote the same offer. You won't see a single e-mail.
Also it will be hard for you to find a job since you are new in this field. Just be persistent, offer something unique and bid for many projects at the same time.
Hope this helps!
Best regards,
DrJale