In order for a new word to be maintained in your vocabulary you must

Hello!

In order for a new word to be maintained in your vocabulary, you must USE it.

This means that if you use a certain word quite often when you're writing, speaking, etc. you'll start to better understand it.

Of course, defining it, pronouncing it, and reading it can also be helpful. The correct answer is "use", though.

The last one i think

What do you mean determine? answer in comment section.