Before you create your first TOS field, you need an article to link to. Review the GDPR guidelines for specifics, but the general idea is that these terms are simple and easy to understand. The best example of a term would be a single, short sentence. This article you are creating is a slightly longer description of your term - but again, keep it simple or you may run afoul of the intent of this portion of the GDPR. The simple version of your term will be used as the field label during registration and will trigger a popup/modal window containing the longer terms article.
How you organize terms on your site is up to you, but I encourage you to have a system of organization. Additionally, you should consult legal council before altering any term article that any user has already consented. Doing so may render the previous consent void. Please consult with legal council. My suggestion is to amend terms with additional terms, but never alter terms unless resolving a typographical error.