When you see something like "51p0" that means that the measurement units are set to picas, not to inches.
You can go to InDesign preferences (under the Edit menu in Windows or the InDesign menu on the Macintosh), and in Units & Increments, change your units to inches.
I saw another of your postings, and it looks like you're taking a very hard road with no tutoring, no class, or no book.
As a total beginner, it will be worth it to spend $20 and order "InDesign CS5 Visual QuickStart Guide" by Sandee Cohen. She takes you step-by-step through what you're painfully trying to learn on your own. I highly recommend it!
Your questions so far are about the most simple and basic features of what is a very complex and intimidating program. If you truly want to achieve useful results from InDesign and tap even a tenth of its potential you will need more help that occasional or even frequent posts to this forum can supply. Have you even tried to read the help files?
As I said on another post, you need to get some training. The cheapest and best option you should consider is InDesign Visual Quickstart Guide by Sandee Cohen.
Hi. I am a 74 year old retired engineer, just starting to learn Indesign. I cannot seem to get even started. When I do a "New" document I am presented with a page where in to define the dimentions of the page. The width says "51p0 and the height says 66p0 for a letter size. What does "xxpx" mean and how do I convert it into inches? Is there a default I can set to make all dimentions in inches?
I've known the same feeling in many applications that I've become proficient in after lots of bashing at the learning curve.
I often suggest that folks search Google for the best description they can come up with for the problem they're having, and to include the application name in the search phrase. In this instance, the search phrase "InDesign set page dimentions," without quotes, presents a bunch of good leads. Google also corrects the spelling to "dimensions." The search phrase "InDesign set page dimentions free online tutorials," without quotes, homes in on useful sources of free training. I'm using quotes here to mark the phrase, but only use quotes around search terms in Google if you want to find the exact term or phrase; case does not matter.
Google finds material all over the Web, as well as at Adobe's site; you'll find other good InDesign information locations with searches that include "InDesign."
In this specific situation, you're asking how to change the units of the dimensions, but it's not the first thing that came to mind. Searching Google for "InDesign change dimension units," without quotes finds a bunch of applicable links. By the way, (BTW) often the Google net finds CS3 and CS4 material, as well as CS5; often the earlier release information is applicable, but sometimes not. If you follow, say, a CS3 link that opens the official online Adobe InDesign help, you'll often see links to CS4 and CS5 help, on the topic page. If the link doesn't open the specific topic you need, enter the found topic's heading into the search box on the newer release's page.
One cool thing that InDesign developers could do to help everyone, not only new users like yourself, would be to enable the dimension areas in setup, and other dialog boxes, with a pop-up tool tip that says something like "you can type the units you want, like ", in, p, pt, here, and change the units permanently in InDesign's preferences."
As a new user, you'll run into many stymies. Once you learn a solution, it's easy to forget those frustrating operations, but you can help smooth the way for future new users by filing formal requests for feature improvements, and new features, here: wish. User requests often are adopted in future product releases, especially when many folks make the same or similar requests.
Have you done any kind of design or layout work with other popular software like word processors, chart makers, publishing tools? Were there any layout and/or publishing features in the software tools you used in your engineering work? Perhaps some of the similarities will help you transfer skills to InDesign, though, some folks find that old ways hinder crossing over.
Above all, don't hesitate to ask questions here. We're all volunteers who are giving back to the community the same kind of help we received when we were beginners.