Let's talk about the imperative in Japanese: an imperative is a way to give orders and/or commands. However, the form of these utterances decides whether they are humble requests to barked orders.
You can find a quite complete reference here
In general you can use a number of forms:
なさい: this is a polite yet firm request. It is often used to soften orders, between parents and child or boss/employee.
ください or noun+
ください: This also a polite way of expressing a request, think of "Please do this". This is widely used, I hear it all the time in classrooms:
The imperative form that is made from either turning the last syllable of a godan verb to the corresponding
e pair or by adding
ろ to the stem of a ichidan verb. This one is used for strong orders, such as those you give to your dog:
There are other variations, but these are the main imperative forms. Note that the て-form is one imperative form among many others. Usage of those forms depends a lot on the context, mainly the current situation and relationship between the speakers.
An interesting example is
頑張｛がんば｝る, to do one's best, to strive for perfection.
- 頑張りなさい would typically be used by soccer moms encouraging their children.
- 頑張ってください would be used to encourage a co-worker.
- 頑張って may be used by friends encouraging you
- 頑張れ (often written ガンバレ) will be used by sports fan cheering on their favorite team/player.
Unfortunately there is no set rule, so it will take some time to recognize in which situation which form of imperative is to be used.