When you don't konw how to deal with the problem, and you ask others for help. Just like "How to deal with it?" "What should I do?" AND sometimes we use it when we have done something wrong or terrble things. 不知所措的时候，常会说“怎么办”。 是一种口语说法。 It's an oral sentence.

“怎么办”means,you are very willing to do something,but you have nothing to do with it ,so you are worry,then may be you will ask youself or others "怎么办". for example:If I get off the train on the way to make one day stop-over, and then go ahead, what should I do? (the sentence "what should I do? " means "怎么办")

how can we deal with ( something).

what shall i do or what shall we do

what can I do