There's not really enough information in your question for anyone to give a specific answer. "hook it up" how, exactly?
If you're talking about using one amp to boost another by connecting the speaker outs of one to the line inputs of another, then the answer is you don't. You'll kill the second amp doing that. If you're looking for more power then by a bigger amp.
If you're talking about splitting a signal to drive some extra speakers, then the answer depends on what exactly you're trying to do and the makes and model numbers of the amps involved. You should post another question or edit this one to say very specifically what you're trying to achieve, and also include the makes and models of any gear involved.
