There are different ways you can do what you want. One way would be to use a track, or clip, volume envelope. First create the envelope. I recommend expanding the track to make it bigger. Then select the portion of audio you want to remove. You may have to turn off snap to grid depending on where the portion is and how big it is.
Then Right Click the envelope line and select Add Nodes At Selection. This will put nodes at each end of the clip. Then just click and drag the line in between the nodes to the bottom of the track. If you want the transition to be smoother you can insert addition nodes by right clicking the envelope and selecting add node, or double clicking the envelope line.
Another way would be to select that portion of audio you want to remove and then go to Process>Audio>Gain and use the Mute preset.
Another way would be to split the clip to either side of the segment of unwanted audio and then click the middle/bottom edge of the clip until the cursor becomes a rectangle. Then drag it to the other side of the audio you don't want.
If there is silence at either end of the segment there is no reason to use a crossfade. Crossfades are for blending two audio clips together. If you want to silence a portion of audio they may not be the best tool for the job.
If you need to use a fade to smooth out the transition from good audio to silence, select the clip so that the selected segment is inside the noise section and there is a small portion of noise included with the good audio. Then Right Click the selected portion and click Split. In the options box that opens select Split at Selection. You could also split each end individually. Then delete the noise clip in the middle. Or slip edit it smaller and use the envelope, or gain, method described above to make it silent. Then click each end of the clips to the right and left near the top so the cursor turns into a triangle. Click and drag the corner until you have the fade in/out you want. Right click the little triangle to change the glide slope.
You could also try splitting the clip in the middle of the unwanted section and then slip-edit the ends and use fades to hide the noisy section.
These are just the ways I would do it, I'm sure there are also other ways to accomplish the same task.