Bab.la is a bilingual dictionary for 28 different languages. Their site includes quizzes, games, grammar lessons, phrasebooks, and a forum for users to discuss language learning. You can also look up various verbs in the conjugation tables or find synonyms and examples of how to use words in context.
Their quizzes should be taken with a grain of salt — If your purpose is to familiarize yourself with vocabulary and grammar structures, then these are probably a fun way to explore your target language. However, if your purpose is to understand the target language’s culture, beware of any quiz that touches on romance, as the advice is similar to that of the magazines found in grocery store checkout lines.
Bab.la may be okay for general definitions, but other sites will probably help you dive further into different languages. Linguee provides examples of words in context sourced from articles and research papers in the target language, and Forvo has millions of words pronounced by native speakers in hundreds of languages. Also, check out WordReference (for a more relevant database of example sentences), Pleco (for Chinese learners), or SpanishDict (For Spanish learners or Spanish-speaking English learners).