There are thousands of resources for learning Latin. A good free course that I often recommend on this site in threads like this is Linney’s Latin Class (
http://www.linneyslatinclass.com/). The lectures are extremely thorough, and the textbook is available as a free download found on the website. You can buy it from amazon if you prefer to hold a book in your hand though. This course focuses on classical Latin, specifically teaching you to read Caesar, but you will get a solid foundation in Latin grammar and vocabulary. William Linney also sells his own very basic, but fantastic, textbook, which is geared towards self-teaching learners. Free audio clips in both classical and ecclesiastical pronunciation are available on that website as well (
http://www.gettingstartedwithlatin.com/), and you can access them without buying the book. You can use the book as a primer to the free course, but you don’t have to.
As far as specifically Ecclesiastical Latin, the best free resource is probably the tutorial for priests on how to offer the TLM available from the Canons Regular of St. John Cantius (
https://sanctamissa.org/en/tutorial/ordo-missae-0.html). It won’t give you much in explicit grammar, but it will tune your ear to EL pronunciation and help you learn what is going on at the TLM, if you are not already familiar. The rest of the website is a gold mine of information on traditional spirituality and is worth reading in and of itself.
Those are probably the better free resources. I would recommend using them together, as one gives you the foundation in the language and the other shows you a classical language in action.
Textkit.com is also a great resource for free books in Latin and Greek, but there’s not much in the way of hand-holding. Beyond that, check your local library and the plethora of Catholic sites that contain audio and texts for prayers. Let me know if I can recommend anything else.