Hi Katie.
I don't know anything about the app I'm afraid,so I can't advise there.It depends on how you wish to approach the task.
I take it since you have created this thread you are not content to concentrate solely on lyric creation? It's my impression that a fair few songwriters are more likely to suffer from lack of inspiration with lyrics,than with composing music,so in theory at least there ought to be a ready made market out there for your words.
If,however,you are planning to be self sufficient,then this poses a series of different dilemmas.
If you have a good ear it's possible to record a melody to fit your lyrics on a phone.At this point you need to be able to put suitable chords to the melody,which again will entail a minimum of both knowing an instrument and having a good enough ear.
In the short term,at least,I believe you'd be best served by working with other musicians and learn from how they bring together your words and either yours or their music. After you've been through that process a few times you'll be better informed as to whether you want to invest time and energy into learning an instrument yourself.
Rather than looking at the whole seemingly insurmountable problem from where you now stand,take it one step at a time and make the journey enjoyable,then before you know,you'll be miles up the road.