Sometimes You Really Must Do Something

ないといけない pretty much means 'must do something'. The something here is a verb and it can be any verb that makes sense in the sentence "You must ___". Remember that in Japanese, the sentence structure is Subject, Object, Verb (SOV) so you can construct your sentence normally and just add "must" at the end. If I were to deconstruct the phrase it would be Verb+ない and といけない where the verb half means "don't ___" and the other half being "don't do". So just like math, we have two negatives become a positive and it equals "must do ___".

 In order to make this sentence you need to know the casual negative form of your verbs.
あげる　→　あげない　To give
勝つ　→　かたない　To win
負ける　→　まけない　To lose
行く　→　いかない　To go

After you have your negatives, simply add といけない and you're complete!
あげないといけない　→　I must give
勝たないといけない　→　I must win
負けないといけない　→　I must lost
行かないといけない　→　I must go

If you would like to use "must" in a formal setting, the proper, more formal way of saying must is なくちゃいけません。

What would Japanese be without shortening long sentences? Simply removing といけない will mean you can't do something. So there is a completely new grammar point that has the exact same meaning but it's better because you will be able to shorten it. Instead of ないといけない, use なくちゃ which comes from the formal version.

あげなくちゃ　→　I must give
勝たなくちゃ　→　I must win
負けなくちゃ　→　I must lose
行かなくちゃ　→　I must go

See how much space you can save by using the shortened version?  In any case, I hope you have fun telling people they must do something in Japanese.