Can your internet provider spy on you if you have a VPN?

Can you explain, in simple terms, whether or not my internet provider can still spy on me even if I'm using a VPN? I've heard that VPNs offer a certain level of privacy and security, but I'm not sure if they completely protect me from my internet provider's prying eyes. Is there any way for them to bypass the VPN and see what I'm doing online? And if so, what steps can I take to ensure my online activity remains private?