Composing a song can be challenging, especially if it's not your natural gift or it's your first time. Depending on the level of musical intricacy you're seeking, you might be in for a real endeavor. If it's your goal to write just any song, you can do so simply by adding lyrics to any tune you make up.
Instructions
1. Learn some music theory if you can, but not so much that you don't lose your creativity and become stuck on the rules. Sometimes the best music just happens and is better because it doesn't follow rules.
2. Start with whatever comes to you first. Sometimes a tune pops into your head, and sometimes lyrics. Remember, you don't always need lyrics to make a song. You can use "ahhs" and "oohs" or nonsense words. To compose a song, all you really need is a melody and some vocalization.
3. Experiment with adding beats, harmony and instrumentation into your song. If you have a good keyboard, this is easy to do but requires special software. If you have only one instrument, find other skilled musicians who can pick up as you play what you have so far.