This summary is not the rule. The rule text controls.
Here's a plain English summary of this rule:
The Board of Governors runs the day-to-day business of the Oklahoma Bar Association whenever the House of Delegates isn't meeting. Think of the House of Delegates as a larger group that sets big-picture policy, but they don't meet all the time. So the Board steps in to keep things running smoothly between those meetings.
The Board also has to handle any extra jobs given to them by either the Oklahoma Supreme Court or the House of Delegates. This means the Board's job duties aren't fixed forever. They can grow or change if the Supreme Court or the House of Delegates decides to hand them new responsibilities.
For anyone dealing with the Oklahoma Bar Association, this rule explains who's actually in charge on a regular basis. If you have questions or issues that come up outside of official House of Delegates meetings, the Board of Governors is the group handling those matters.