Waiving criminal records and unlawful presence
Committing a crime in the past makes you inadmissible to the US. In general, you will be refused entry to the US and will be denied a visa or a green card. However, it is possible to be excused for this (to receive a waiver) and get you a visa or green card. Only misdemeanor (for example shoplifting) convictions can be forgiven. Felony (such as murder) convictions will not be waived.
On a different note, if you have stayed in the US undocumented (thus violated immigration rules), you can apply for the provisional unlawful presence waiver. Such a waiver may be applicable in cases of family-sponsored immigration, employment-based immigration. Each case is individual, a consultation with an immigration lawyer is strongly advised.
Biometric data (fingerprints) is taken at a USCIS field office as a part of waiver application submission. If case of submitting documents by mail, the applicant receives instructions where and when to attend a biometrics appointment.
Processing time for waivers may be up to 1 year. The applicant may request an update after 130 days from the application.
A qualified lawyer can assist with preparing and submitting the waiver. Do not do it yourself.