There are several ways:
1) Add it manually: go to My dictionary - enter the word in the search bar - select a translation or add your own - the word will be added.
2) From Jungle contents: click on a word - select a translation or add your own - the word will be added.
3) From word sets: go to «Dictionary - Word sets and Phrasebooks» - select the topic you're interested in - add the whole set or just the words you need.