As the title tell, I am having some problems finding my way in these digital books. 

I am trying to set up an adventure, and at times the set up - sheet refer to specific pages in Basic Rules, Monster Manual ect. As an example I tried to find a simple "Guard" in the Monster Manual, page 347. There is no Guard in the digital version as I can tell. 

I did find it simply by searching, but I do not know if it's from the right book. That information does not include on the page I find the Guard in. 

I am really new to DnD, and I wish things were easier to find.

Do you have anything that could help me with this problem?

Thanks, PH

Welcome to D&D!

I apologize for the long section of bold/italic text below.  I was trying to just italicize the names of a couple of sources, but the editor is glitched and won't let me turn it back off again.

I'm not sure what you mean by a set-up sheet for an adventure. I take it that you are not using an adventure published by Wizards of the Coast and available here?  What adventure are you using?

Somewhere around on the forums is a link to the word someone did providing page number references for lots of things in the book; I'll see if I can track it down and if so I'll post it a bit later.

I'm not sure that guide would help you in this particular instance.  So let me address the example you provided.

The best way to find the "monster" in question is to use the Monster listings available under Game Rules>Monsters in the menu at the top of every DDB page.  Type in the name of the monster (in this case Guard) in the Monster Name field, then click "Advanced Filters" and in the Source field (not source category), begin to type Monster Manual.  Before you are finished, it should show up as an option to select.  Now hit the filter button.  Then you will get a list of monsters with Guard in their name that appear in the Monster Manual.

If you follow my instructions, you may notice, however, that when you look at the list, all of the entries that show up have "Basic Rules" in italics under the name of the monster, and not Monster Manual.  This is because Wizards of the Coast released a couple of free PDFs, the Basic Rules  and the System Reference Document or SRD.  DDB has combined the contents of those two documents, and  called them together the basic rules.  Every  monster in the basic rules is also in the Monster Manual.  But not every monster in the Monster Manual is in the Basic Rules.  [If, for example, you change "guard" to "orc" in the Monster name field and hit the filter button again, you can see what i mean, as a regular old Orc lists Basic Rules as the source, but the Orc Eye of Grummish and the Orc War Chief list the monster Manual.]

You can do the same sort of thing with spell and magic items listings.  With rare exceptions, there should only be one monster/spell/magic item with a given name, and most of those exceptions are clearly marked so you can tell the difference.  Note that with both spell and magic items, there are items that are in the basic rules that are also in either the Players Handbook (spells) or the Dungeon Masters Guide (magic items).

If you were using one of the official published adventures here on DDB, the entry for guard would have been linked like this: guard, and you could have just clicked on it to see the statblock and info, and thus no page number needed.  There is absolutely nothing wrong with using adventures from elsewhere--I do it all the time.  They just don't have the advantage of the linking.

I hope that was helpful.  If there are other things you are finding challenging or are uncertain about, please post again and any number of people here would be happy to help you.