Hi, Ela. On Windows, you can use the Chrome browser and install the "Google dictionary" extension. After that, you can either double-click on any  unknown word to see the meaning, or select + hotkey to see translations of whole phrases.

If you're on a Mac, just tap with two fingers on any word (or force-tap on newer macbooks) and select "look up" from the pop-up menu.

If you're on iOS, long press any word and select "look up" from the pop-up.