Filing a will is an easy process. Go to the Clark County Superior Court Clerk (located at 1200 Franklin Street, Vancouver, WA 98660), and bring the original Last Will and Testament with you (keep a copy for your records). If all you are doing is filing the Will, and not opening a probate--there is a $20 fee to file the Will.
If you are going to initiate a probate action, then you should speak with a knowledgeable probate attorney to assist you in preparing the necessary pleadings to have a personal representative appointed. If you are not sure whether you need to initiate probate, I would recommend speaking with a probate attorney who can help you analyze your specific situation.
The above response is commentary regarding a general legal question. It is not intended to be legal advice specific to the reader's individual situation nor does it create an attorney-client relationship between the author and any reader. You are encouraged to contact a qualified and knowledgeable attorney to discuss your specific legal situation.