There don't seem to be a whole lot of good resources online to learn Guarani. Recently a colleague sent me a link to LearnGuarani.com, a site that's under development by Stephen. So far so good. I'm hoping this will develop into a useful resource for beginning Guarani learners.
If you want to learn Guarani not just as a linguistic exercise--that is, if you're interested in actually communicating with mother-tongue Paraguayan Guarani speakers--you need to keep a couple of issues in mind:
First, there's a movement to "purify" Guarani by removing as much Spanish vocabulary from it as possible. There is a sense in this movement that Guarani is somehow weakened, corrupted, or made less beautiful by the inclusion of loanwords. Whether that is true or not is a subject for another posting, but suffice it to say that if you want to use a Guarani that actually communicates, you should focus on "Guarani-Jopara," (mixed Guarani,) or Paraguayan Popular Guarani, which does include a lot of Spanish loanwords. The words that academics have either created to reference new concepts or revived from archaic sources will leave most Paraguayan speakers perplexed and instead of promoting relationship will tend to increase distance between you and your listener.
Second, if you are learning Guarani with a Paraguayan Guarani-speaker as a resource, generally speaking he or she will not be confident about writing in Guarani. Paraguayan children now learn to write in Guarani in school but this wasn't always the case. I do not mean to suggest that Paraguayans are illiterate but most adult Paraguayans feel much more confident reading and writing in Spanish than in Guarani, even if Guarani is their first language. Unless your Guarani resource person has studied Guarani, either he/she will be reluctant to tell you how to spell things in Guarani or he/she will spell it in a way that diverges from the accepted orthography.
For this reason you are likely to come across a number of different spellings for the same word, such as: jaé, jhaé, jha'e, or ha'e, (meaning he/she/it,) only the last of which is written in the currently accepted way. (Just look at any map of Paraguay and you'll see a dozen Guarani place names spelled in an orthography based on Spanish that is diferent from the current official orthography!) This can be confusing to the beginner but it's by no means insurmountable. You have to learn to hear the sounds and transcribe what you hear. With practice you'll do this with little difficulty.
If anyone comes across any good online resources for learning Guarani-Jopara, I'd be happy to know about them.