Is ProtonMail free?

Excuse me, could you clarify something for me? I came across a mention of ProtonMail and I'm curious about its pricing structure. Specifically, I'd like to know if ProtonMail is available for free, or if there are any fees associated with using its services? If it's not free, what are the various pricing plans they offer, and what features are included in each? I'm keen to learn more about this service and how it can benefit me.