A phrasal verb is a verb usually followed by a preposition. The difference between an ordinary verb followed by a preposition (eg look at a word) and a phrasal verb (eg look up a word) is that
the meaning of the former can be easily understood once you know the meaning of the base verb (in our case it is the meaning of the verb look), whereas the meaning of a phrasal verb oftentimes has nothing to do with the meaning of the base verb. If you look at a word, you use your eyes to see the word, if you look up a word, you find what it means by consulting a dictionary.
There are two-part and three-part phrasal verbs, the former are verbs followed by only one particle, adverb or preposition, and the latter, as the name suggests, are followed by two of those.
There are some Quizzes on Phrasal Verbs, Dependent Prepositions & Prepositional Expressions on EnglishLab.Net for phrasal verb fans. If a quiz seems somewhat difficult, feel free to visit the Online Reference Section (it will open in a new browser window) and look up the phrasal verb or prepositional expression you are unsure of in an online English-English Advanced Learners' Dictionary such as LDOCE, OALD or CALD.