I heard that it is possible to get a waiver of inadmissibility (pardon) for being here illegally, without leaving the U.S. Where can I apply and how.
The answer to your question is information that many must have. It is most important to understand that although the benefit you mention has been announced, it has not yet been implemented. This is because the US Citizenship and Immigration Services (USCIS) has not yet published the procedure or the evidence that will be required to determine qualification to applicants.
Your facts refer to the provisional waiver, to be filed on form I-601. This procedure is not yet available, but it is getting close. Before such new procedure is implemented, it must be published in the Federal Register with a comment period offered to the public. This has now been completed, but the final regulations have not yet been released. Unfortunately, this process too is subject to abuse by scam artists and those eager to make fast money. In this area too, the USCIS has taken steps to warn the public. Keep in mind that anytime you become a victim of a serious violation of law, it is important that you report the matter. Being a government witness may also qualify your for an S or U visa, provide employment authorization and possible green card status.
You must also understand that all offered benefits have exceptions to eligibility. Each case must be analyzed to assure that the application will not result in a denial, because denial can in may instances result in referral of the case to Immigration and Customs Enforecment (ICE) and Immigration Court for removal proceedings. Only an experienced immigration lawyer can best determine whether your case is likely to succeed, and if not, at least inform you of the consequences of denial.