Overdescribing is when you use several additional words or sentences to say the same thing. 
For example:

He always takes control of every situation. That's just how he is. His manner. How he likes things to be. 

As you can see, the information needed is "He always takes control of every situation." The addition of "That's just how he is" is not ideal but also not a terrible thing as it's giving extra information on the character. However, the next two sentences are just reiterating what has already been said. Therefore, absolutely not needed. 

Now, I do understand that sometimes this is done specifically for emphasis, and quite often for humour (obviously not in the example above), and that is fine occasionally. As long as you aren't doing it so many times that it's making the writing clunky and slowing down the pace too much. 

Another less wordy example of Overdescribing is:

She shouted loudly.

and

The sun was hot, scorching, burning my skin.

There are a couple of ways to tackle "She shouted loudly". The thing is, a shout is loud by definition. So "She shouted" is fine. To be more descriptive, you could use synonyms such as "bellowed" or "hollered" instead. 

And then with the second example... you don't need to use "hot" AND "scorching" AND "burning my skin." Instead, "The sun burned my skin."

The more mindful you become of this, the easier it will become to make your first drafts that little bit tighter - and - of course - save you a little more money on edits!