You are going to have to get hold of a teach yourself MS Word program to become proficient in Word, or have a friendly secretary to advise (that’s how I learnt).
Where you have pages requiring an alternate format (such as 2 columns, or landscape rather than portrait) within a document, you need a Section break both before and after (with the formatting within that section as required). The sections before and after may also need the format set as required.
If a document is so set, and you delete a Section break, Word may now apply the settings in that section to the remainder of the document – causing the type of problem you are experiencing.