You can use PicMonkey for free after registering with your email address. You will not have access to paid features, and you will not be able to share or download any of the images you create in PicMonkey.
You can use the PicMonkey Mobile App for free. See: Does PicMonkey have a mobile app?
To learn more about the types of PicMonkey subscriptions available, please visit: Basic vs. Pro PicMonkey Subscription Plans or see the PicMonkey Pricing page.