So Melly,
There are actually two ways to do it. If you think of it as having 3 chunks of audio it makes it easier to visualize.
The first chunk is the area before the one you want to keep.
The second chunk is the area you want to keep.
The third chunk is the area after the one you want to keep.
|--1--|--keep(2)keep---|--3--|
So, option #1 is to highlight area 1 and hit "Delete"
And then highlight area 2 and hit "Delete".
This tends to mess with the original, which I do not recommend.
The alternative and probably easier way to do it is to simply select (click and drag to highlight) the area you want to keep. And then hit Cntrl-C to copy. And then to "File" > "New" to create a new project. And hit Cntrl-V to paste it into the new project. That's how I do it, because that way you don't mess with the original.
Let me know if you need a tutorial video, I can make one if needed.