Thanks for your interest in CiviCRM.
As Peter says, a good place to start is to read the documentation. I would also suggest that you look at the CiviCRM website if you haven't already done so.
To answer your specific questions:
- Anyone can implement a CiviCRM system. The software is open source and feely available to download. However, it does require a reasonable degree of technical knowledge to do so. For this reason many organisations choose a partner to do this for them. You will see that there are partners around the world. But, if you want to do it yourself read the Installation guide.
- CiviCRM is used by more than 10,800 organisations including the Wikimedia Foundation, Amnesty International and the UK Green Party. Take a look at the many case studies to see some examples.
- I would suggest that you try a web search for comparisons with other CRM systems. Whether it is suitable for your organisation depends on how you would use it. It is difficult to comment on this without more detail about the needs of your organisation.
- CiviCRM is specifically designed for the needs of non-profit organisations. But there is nothing to stop it being used in other sectors and much of the core functionality would be appropriate for any organisation that is looking to manage contacts.
I hope that helps, but please post again if you have more questions.