My iron is a steam iron and I put h2o in it to...

Question

My iron is a steam iron and I put h2o in it to create steam. I let the h2o sit and now when I turn it on I get a brown mist coming out of it. I tried to let the iron steam until it was out of h2o, but it did not work. I was once told that you could clean an iron by putting vinegar in it and letting it steam out. Is this true?