The period gives your thought a hard stop before beginning a brand new, self-sustaining sentence. Think of it as an extended pause between the two. It should be used at the end of just about every sentence that’s not a question. (Unless it’s a title case headline.)
Not sure if you have a sentence? There should be a subject and a verb, maybe even an object. If it’s not a complete sentence, it’s called a “fragment.” In marketing or long-form copy, we’ve been known to allow fragments for stylistic reasons. (Reach out to #writing-at-hudl in Slack if you need advice.)
And as you’ve seen in this section, there’s no need to add two spaces after your period. We’re not writing on typewriters anymore, so a single space is all you need.