The posts linked below describe the craft of notating music. This is relevant to composers in the same way that learning to type is useful to novelists. For assistance with the art of composing or arranging, seek help elsewhere.
How do I start writing sheet music on my computer?
How do I efficiently write sheet music on my computer?
What does typing sheet music on my keyboard look like?
How can I efficiently add slurs and ties to my sheet music?
How can I efficiently add dynamics to my sheet music?
How can I name every page of my Sibelius scores?
How can I turn my sheet music into a book?
How do I read this LilyPond file?
How do I edit a LilyPond file?
How do I transpose a LilyPond part?
Can I import a LilyPond file into my graphical notation editor?