"Check it" makes sense to me. But I don't understand the meaning of "check it out". It is not the only case. In many cases, the addition of "out" makes the sentences/phrases awkward to me, though this type of sentences/phrases are available in English movies, such as "David held the box" makes sense, but if I add 'out' after the word 'held out' (David held out the box) does not make any sense, i.e I can not understand the meaning.
Please, help me to get rid from this problem.
Best Answer
"Check out" in this case means to go look, see, inspect, examine, etc.
e.g.
"Check" simply is to inspect or examine or verify, among other senses.
http://dictionary.reference.com/browse/check?s=t
https://en.wiktionary.org/wiki/check_out
"verb + out" constructions are a type of phrasal verb, which are often idiomatic and their meanings are not connected to the first verb the same way each time. (You'll have to find out those meanings) English speakers use them a ton, gotta deal with that.
Often translating a phrasal verb will take up a different amount of words (maybe one word or so) in a destination language. (e.g. "to look for" is translated as "chercher" in French.)