The New York Times has an explainer:
The vote is on a resolution that would set rules for the public phase of an impeachment inquiry that has so far been conducted exclusively behind closed doors. It would authorize the House Intelligence Committee — the panel that has been leading the investigation and conducting private depositions — to convene public hearings and produce a report that will guide the Judiciary Committee as it considers whether to draft articles of impeachment against President Trump.
The measure would also give the president rights in the Judiciary Committee, allowing his lawyers to participate in hearings and giving Republicans the chance to request subpoenas for witnesses and documents. But the White House says it still does not provide “basic due process rights,” and Republicans complain that their ability to issue subpoenas is limited. They would need the consent of Democrats, or a vote of a majority of members. That has been standard in previous modern impeachments.
More details are at the link.