some of the pages only have one surname, and the rest of the lines have DO, what do you do here.
DO is a variation of the word "ditto", so if you have "John Smith" then "DO", you will only index the first John Smith.
As @erutherford mentioned, DO Is an abbreviiated form of “ditto,” meaning “same as above.” So, if it is used in a column of Surnames beneath the Surname Smith, then in each place where you see a DO you can substitute Smith.
Whether you index all the Smiths or just the first depends on differences between their Given Names and other indexable fields, and the instructions regarding indexing duplicate names for your batch/project.
On the batch I am doing, the Surname is on the Left side, below it indented is the first name, but some lines only have "Do" indented, below it, sometimes more than once, with other lines have names. Do I just ignore the Do as a ditto?
"Do" means "same as above." You don't ignore the "Do," you act on it and replace the "Do" with the text/name (Surname or Given Names) above. Or, if you have a whole list/column of "Do," you look to the name above the first "Do" for what name to substitute for each of those "Do"s. You do not Index the "Do" itself.
If you have a question regarding a specific batch, please post the Batch Code - the letters and numbers at the end of the Batch name. It looks like [MXXX-XXX]. Then someone can give you the most accurate answer by looking at your batch and its instructions and examples.
I'm not sure what John means by his answer. If fifteen 'Do's are listed immediately under John Smith what then.
“Normally” that means that each of those “Do”s can be replaced with “John Smith.” But it’s still best to share the Batch Code so a helper can ensure there is no odd situation going on that works contrary to the “normal” meaning of what you described.