"a firsthand understanding" is correct and can be used in written English.
It is used to describe someone's knowledge of something based on personal experience. For example, "He had a firsthand understanding of what it was like to live in poverty after spending time volunteering at a homeless shelter."
To do this, I needed a firsthand understanding of the horses' physical condition.
Several said they wanted to begin 2002 at ground zero to have a firsthand understanding of the tragedy.
Untainted by the district's political infighting, Ms. Palma -- a single working mother -- has a firsthand understanding of the area's needs and the skills to get results.
Basic to the experiential approach is the belief that it allows for a firsthand understanding of religion as an actual force in human life, in contrast with religion taken either as church membership or as belief in authoritative doctrines.
As the chief executive of a multinational corporation with operations in three dozen countries, Mr. O'Neill brings to the Treasury Department a firsthand understanding of how currency fluctuations affect the economy.
I think the fact is that when you really think some of our "treasures" of the season probably have many origins within pagan traditions, that gives you a firsthand understanding of the fact that pagan traditions are beautiful traditions.
While motherhood can give an elected official a deeper firsthand understanding of issues, it also siphons off time from the fund-raising and handshaking crucial to moving on to higher office.
"We thought that by participating, we'd gain firsthand understanding of those limits," says David, now an assistant professor of molecular genetics and microbiology at Duke University in Durham, North Carolina.
He also began to have love affairs with fashionable or aristocratic women at this time, finally gaining that firsthand understanding of mature women that is so evident in his novels.
Although Nguyen does not feel confident that this week will bring justice for the people he met along his journey, he is confident that if the world leaders had the firsthand understanding of the situations he experienced on his ride, the negotiations in Copenhagen would be a lot closer to strong solutions.
The value of the promotora-delivered education program stems from their direct experience with the community and participants' living situations, support and empathy that often is difficult for professionally trained individuals to provide, and firsthand understanding of the myths, beliefs, and cultural remedies that may interfere with the adoption of health recommendations.
