Hi, I am no keyboard player but had a few piano lessons a long time ago. Suggest you check out youtube, that is where I get a lot of cool ‘lessons’ and how to’s. Try searching for how to play keyboards or piano for a particular song as well as searching for melodica on youtube.
There are also a few apps on android and itunes too I would imagine for how to play keyboards or piano. Before too long you will be sounding songs out and playing by ear. Music theory is great but I tend to learn tunes faster trying to play them by ear.