I'm reading the construction of Adams spectral sequence from Adam's Stable homotopy and generalised homology. The construction of the SS is begun with the following description
We start with $Y=Y_0$. Suppose $Y_p$ has been constructed. Let $W_p=E\wedge Y_p$. Then we can form the morphism $$Y_p\simeq S\wedge Y_p\xrightarrow{i\wedge 1} E\wedge Y_p=W_p$$Construct a cofibering $$Y_{p+1}\to Y_p\to W_p\to Y_{p+1}$$where $W_p\to Y_{p+1}$ has degree $-1$.
I couldn't understand how the cofibration sequence is obtained. If $Y_{p+1}$ is the cofiber(fiber) then how is another $Y_p$ at the left(right) hand side of the sequence obtained?