I'm using Sitecore 9, which has Sitecore Forms built-in out of the box. In the "Form Elements" tools panel on the right, there's a list of elements you can use to build the form. For example: Text, Single-line text, Multi-line text, Number, Email, etc. The Text element only allows plain text, although you can choose from a short list of html tags to wrap in it. It does not allow for rich text, such as adding anchor tags. How do you add rich text to the middle of a Sitecore Form?
You could check the Forms Extension my colleague Bart released: https://github.com/bartverdonck/Sitecore-Forms-Extensions. It includes a "RawHtml" field that can be used to output unescaped pure html.
Or just check that code to create your own version with a custom field that suits your needs (as the raw html is fairly simple). Documentation on how to create your custom field can be found here: https://doc.sitecore.net/sitecore_experience_platform/digital_marketing/sitecore_forms/setting_up_and_configuring/walkthrough_creating_a_custom_form_element