If you build it, they won’t necessarily come. However, you still need a donate now button on your website. You never want a situation where potential donors stumble across your website, yet can’t figure out how to give financial support.
Your button should be in a very visible place and on multiple pages of your website, not just the home page. People enter your site through pages other than Home.
You also need to make it easy for people to submit an online donation. I strongly discourage requiring registration from people in order to give. That could turn away potential donors who simply do not want yet another password. Let them make their donation without setting up an account and offer the option to create an account. Do not require it. The bottom line is giving to your organization needs to be very, very easy.