You can try to use it with free trial. Sign up and get $300 to spend on Google Cloud Platform over the next 12 months.
Google: Professional have much better translation quality than another two variants. But use it is not necessary if you are satisfied with translations created by Yandex: Free or Google: Free feature.
If you want use Google: Professional driver, you need to register your own project and enter your own API KEY in the appropriate field at the "Translate Feature" of the "Settings -> General" section menu.
Google Quick Start article.