How to hide words/phrases from learning?

Select (by long press) all words, which you wish to hide from the training, and then select the icon with crossed out eye, as shown in Figure 1.

Figure 1.

Hidden words are at the end of the category, as shown in Figure 2. You can collapse the hidden section by pressing on arrow up icon.

Figure 2.

If you want to return back hidden words to the training, then select them again and click on the icon with crossed eye.