What was the poet doing at first?

In his Introduction to The Songs of Innocence, William Blake writes in the person of a speaker who has been "piping down the valleys wild." The piper encounters a child "laughing" on a cloud, who then proceeds to make requests of the piper in terms of what songs he is playing. The child asks the piper first to pipe "a song about a Lamb," which the piper does, causing the child to weep in response. The child then requests that the piper sit down his pipe and sing instead, "songs of happy chear." In response to this, the child weeps "with joy."
Finally, the child asks the piper to "sit thee down and write," whereupon the child disappears. Obediently, the piper "made a rural pen" and, using "stain'd" water, writes down the songs "every child may joy to hear."
At the beginning of the poem, then, before he encounters the child, the piper has been simply playing whatever songs of "pleasant glee" came to his mind, with the implication being that he is not playing for anyone in particular—rather, he is playing to "the valleys wild."
https://www.poetryfoundation.org/poems/43667/introduction-to-the-songs-of-innocence