I've registered domains and bought hosting for them but don't know what to do next. can anybody help me in this regard as I'm new to all this? Thanks in advance!
You will need to upload the files you created for your website to your host, this will be done through the control panel, or a 3rd party FTP. IF this is your first time I would just call the hosting company and have them guide you through the steps.
Free templates are a mixed bag. On the plus side you can have your site up and running with a professional layout within minutes, but a negative is that you often have the designer's name and web address plastered somewhere on the site, which can be intrusive.
Nothing wrong with using free templates etc if you just want to get your website online and develop your design for the site in your own time. I would suggest to go to the website support section hosting company you are with and they should have some tutorials etc on how to get started on their system.