how to do that? if it is a e-commerce website, how can we upload such many pages all at once?
That is a more picky question, it depends what CMS you are using, if you mean adding thousands of products to your site, this is not exactly the same as uploading HTML pages.
So the question is, how are you making/managing you site? With some CMS, you have to add products manually, one by one, others can have batch importation tools. Refer to the documentation of your CMS / Software.
The wording of the question implies that youíve got thousands of hard-coded pages which physically exist and are just waiting to be physically uploaded one by one. But surely that isnít what is really going on? If you are asking about taking some action which will lead to the creation of thousands of new URLs, that's an entirely different question.