Do I have a blog?

If you have a personal blog, then most probably you won't be needing an SSL certificate. The blog does not sell any products or services? It has no contact form? It does not require visitors to log in? Then getting an SSL certificate is a waste of your time and money. The load time of your website is likely to grow and the positive impact on SEO that Google may provide is quite minimal in comparison.

Do I sell products or service?

If you have an e-commerce website and you are collecting money directly on your website through credit cards, you will absolutely need an SSL certificate. Not only does an SSL certificate instill trust in your customers thus increasing your sales volume, but it is your responsibility to provide shield to customers' confidential information as a seller. However, you do not need to have SSL all over the website because the web pages will load less fast with the encryption. You can use it on the checkout page or signup page, for instance.

Do I have a form via which the customers submit their information?

If you have a login page where users of your website will need to enter a username and password to log in, you should be getting an SSL certificate. Without SSL encryption, hackers can easily see your customers' username and password in plain text. They may use this information to impersonate your customers on your website. The more dangerous part comes after: most online users use the same set of username and password for many websites, maybe even their bank account. It is the same with the kind of form via which your customers submit a photo, documents or any personal information. If you have one of these forms on your website, get an SSL certificate!