This is the most important point.
It is essential to address each issue raised by the editor and reviewers. Even if you consider that a request is impossible, or unreasonable, or just wrong, you need to mention it in your reply letter and explain your thinking about it.
If you don’t mention all the points that were raised, they are unlikely to ignore omissions. Your manuscript will probably be returned and you will be asked to submit another revision.
To address each issue, you first need to identify all of them. This is sometimes easy because thoughtful reviewers will give you a numbered list of points to respond to, or will set out their questions clearly in some other way.
Unfortunately, many reviewers jam all of their questions and comments together. Then you have to try and disentangle them. Here is a typical example of a letter from that type of reviewer, which I have devised. (See Example 1)