上で (ue de) is used to say that you do something after doing something else first, or that you make a decision after considering a previous step. It often implies that the first action is a necessary preparation or basis for the second. For example, you might say 話し合った上で決めます (I'll decide after discussing). This is a fairly formal pattern, common in business or written contexts, but can be used in spoken Japanese when you want to sound careful or deliberate.

It can also mean 'in order to' or 'for the purpose of' when attached to the dictionary form of a verb (e.g., 使う上で便利です = convenient for using). That usage is more about the circumstances or purpose of an action, not about time sequence. But the most common N3 meaning is the 'after doing' sense.

A key point: the verb before 上で must be in the past tense (plain form) to express sequence, not the present or te-form. So you say 確認した上で, not 確認する上で (which would mean 'for the purpose of confirming').