Go to recreation.gov. This website is designed for making online reservations for federal parks.
Click on "Sign Up" underneath the top navigation buttons on the website. You must create a free profile before you are allowed to register.
Fill out the form to become a member. The form will ask you to include an e-mail, password, address and phone number. When you are done filling in the information, click on "Create Account" at the bottom of the form.
Click on the "Home" button on the top navigation panel.
Fill out the "Reserve Your Place Under the Stars" form on the left side of the homepage. Click on "Search" when you are done with the form.
Click on the "Tillicum Beach" search result that appears on the page. The next page you will see gives you all the information about Tillicum Beach including rules, amenities and important information regarding the park.
Click on the "Book Now" button on the the right side of the page. The button will lead you to the options available during the dates you requested.
Click on the date and location that you want to book. You will need to click on "See Details," which will give you more detailed information about your reservation. Click on "Book these Dates" at the top of the body of the page.
Fill out the "Order Details" form. This will let the park know what equipment you are bringing and how many people will be at the site. When you are done filling out the form, click on "Add to Shopping Cart," which will take you to your reservation with the reservation fee and camping fee.
Click on "Checkout Shopping Cart," which will take you to a page to fill in your payment information.
Fill in your payment information. Click on "Complete this Purchase" at the bottom of the screen to finalize your purchase.