I only very recently came to understand bandwidth too, and ran out of it for the first time this morning. It seems that how much you can post on the platform is a factor of how much SP you have. So when you start with the delegated SP for newbies, it isn't enough to do much at this time of day. (Another component is how busy the platform is at the time.) So you have to either buy more STEEM and power up to SP, earn more over time, or just not try to comment or post much during busy hours. This morning for the first time I found my bandwidth at zero and couldn't reply to a comment. Ten minutes later is was at 20% and I could start using Steemit again.