Supposing you want to write more than just instrumental pieces, I'll attempt to show you how to write lyrics. Now, in writing lyrics, ideas come almost everywhere. They can come when your in the shower, walking on the street, playing guitar etc. Now, once you have some sort of lyrical idea and message, it's not hard to evolve into a proper song.
Here is a bit that just came into my head
It seemed like one of those days
Where I hope everything would change
Now, think of something to "answer" the first bit.
But in the end
It's still the same
The status quo still contends
This shall be the verse. Now when writing songs, the verses must link up to tell the story.
Here's an example of a second verse
It seemed that once again
I'm abandoned then
I hope that one day
I can lay
Myself unto happiness
The chorus' job is to say what you feel about the verse. Something you can about the whole song together.
I just want to continue
For another day
I just need help
To find another way
Please don't turn you back
It's your smile that I lack
And please help me to go on
One you have written all your lyrics, experiment with some chords to play over the song to inspire a melody. After that, you can add riffs, run, solos etc. to your song.
Here's an example of a mini-song
It seemed like one of those days
Where I hope everything would change
But in the end
It's still the same
The status quo still contends
I just want to continue
For another day
I just need help
To find another way
Please don't turn you back
It's your smile that I lack
And please help me to go on
It seemed that once again
I'm abandoned then
I hope that one day
I can lay
Myself unto happiness
I just want to continue
For another day
I just need help
To find another way
Please don't turn you back
It's your smile that I lack
And please help me to go on
(Guitar Solo)
I just want to continue
For another day
I just need help
To find another way
Please don't turn you back
It's your smile that I lack
And please help me to go on
I hope this lesson will inspire your lyric and songwriting.