How to apply for H1 visa?

Even though the H-1B visa is a non-immigrant visa, it is one of the few visa categories recognized as dual intent, meaning an H-1B holder can have legal immigration intent (apply for and obtain the green card) while still a holder of the visa. In the past the employment-based green card process used to take only a few years, less than the duration of the H-1B visa itself. However, in recent times the legal employment-based immigration process has backlogged and retrogressed to the extent that it now takes many years for skilled professional applicants from certain countries (like India and China) to obtain their green cards. Since the duration of the H1-B visa hasn't changed, this has meant a lot more H1-B visa holders have to renew their visas in 1 year or 3 year increments to continue to be in legal status while their green card application is in process.