Well the way I see it, it's just about realizing where the market trend is going on multiple time frames, and then figuring out where the next trend is beginning on the time frame you are trading. The market moves in nonstop waves and I trade short term (daytrading) so I look for shorter term moves of course. When the trend is up and MACD is going up, you have a sustained move that will continue, which is called convergence. When the MACD is going down and the market is still going up, you have divergence. That's the gist of it, but of course you have to apply other information from price action to make the right decision every time.
Another question : What wrecked you the most when you just started? For my case, it was learning from a particular trading coach. I took me years to decontaminate my mind, delete/unlearn what I had learnt from him.