Please make certain you understand the difference, too. Take time to polish your mms and query before hitting a query-only publisher. Slushpile discoveries happen, and you can increase your chances with hard work.
As for agent-only publishers, walk away until you have either an agent, or a stunning mms. Say you submit to them anyway, and they reject or ignore you (most likely). If you later try to have an agent submit that same mms to the same publisher...you have not only burned the bridge, but probably the agent.
Baby steps, here. Take it from someone who made a lot of stupid errors in the years before she found AW and other sites, and learned the ropes.