Please we are an organisation who have come up with training manuals. we want these manuals deposited in public libraries in our country. how do we write a cover letter to the Liberians to get the manuals to the libraries?
Many libraries have a local author's section. If you are donating a book, and you are local, you may be able to have it placed there by directly contacting that particular location.
If you are trying to be picked up by a larger library system, they will probably have an acquisitions department. You should be able to get contact info for this on their website, or by calling them.
You can send them a letter promoting your book, but it's unlikely to have much of an impact, since they almost certainly have a set budget, limited shelf space, and a pre-established set of criteria for picking books. If you are donating the books, and can make a good argument for them being of general public interest, it may be worth the attempt, however.