This is a free online class offered by Berklee College of Music through Coursera. The course is 6 weeks long and does require a time commitment, but if you take the time it is well worth it. This may really be a help to get you going further in your songwriting.
I took this songwriting course the last time around, and it was very informative and helpful.
This course will require some capability of recording on your computer in order to submit the class assignments. Most computers have built in mics, and you can download the recording software for free.