Why do I get the error “\caption outside float” with the algorithm / algorithmic package? [closed]

Question

I have an algorithm in my document

It looks like this:

\begin{algorithm}
    \caption{Merge Digest: Insert\label{mergeDigestInsert}}
        \begin{algorithmic}[1]
            [....algorithm is here]
        \end{algorithmic}
  \end{algorithm}

When I compile the document I get this error:

Package caption Error: \caption outside float.

I tried putting the caption inside of the algorithmic block, and I tried to put it at the end. I also read somewhere that I need to declare algorithm as a caption type like this:

\DeclareCaptionType{algorithm}

but when I do that I get this error:

LaTeX Error: ./doc.tex:21 LaTeX Error: Command \algorithm already defined.

I appreciate any help that can be given on this.