Magento is a very good selling platform. Just like with any system you will have to develop a theme.
Magento theme has many components, so it might be worth to do some research and get a theme which is close to the design that you want to have. Modifying that would be far less work than starting from the beginning.
For payments you can use Paypal, if you open a merchant account with paypal you will be able to take credit card payments on your site without visitors leaving your site. Magento has many other payment getaways options so it depends on what you want.
You can get an SSL certificate from most of web hosts. When you apply for a certificate, you will be asked to provide your details which will be attached to the certificate. Once you receive it, from your hosting control pannel you will be able to install it. After that you will be able to use https protocol. This way the data send between the server and client is encrypted which is needed when handling sensitive information (user registrations, password, credit card details)..
Hope this helps, if need anything else, let me know.