SPF (Sender Policy Framework) is a protocol that allows you to control spoofed email.
SPF does not stop spam or increase the likelihood of filtering spam, as you can often read about it in articles. SPF provides a tool for domain owners to declare the authenticity of addresses. This allows you to check email messages for originality.
The point is that there are vulnerabilities in email delivery systems that allow spammers to spoof or steal email addresses. The task of SPF is to prevent spam from such addresses.