To answer your question very specifically: here is the technical documentation for the ACS2012-1yr summary files: http://www2.census.gov/acs2012_1yr/summaryfile/ACS_2012_SF_Tech_Doc.pdf
But, the comments on your question provide sage advice: if you don't know why you need the summary files, you may be better off using the American Fact Finder.
Alternatively, I've been part of a project called Census Reporter, which aims to make ACS data easier for journalists to use. We hope that it's useful to non-journalists as well. Here's our profile page for New Orleans You can also get bulk data for different tables. We're gradually working on some help documents that try to put census concepts into clearer, if sometimes less technically precise language.
If you do want to go deeper with the summary files, the first question is "why do you want data for both the 1-year and the 3-year"? They are not meant to be compared to each other. If you want to compare data for New Orleans this year and three years ago, use the 2012 and the 2009 1-year data sets. If you want data for different areas inside New Orleans, you'll need to use the 5-year dataset to find census tracts or block groups inside the city.
The root of the Census Bureau's ACS documentation is at http://www.census.gov/acs/www/
Just to get a general idea of what goes on in the ACS data, I found the ACS Handbooks for Data Users quite helpful, and there are several versions each slightly tailored to a different audience. Coming from a journalism background, I was impressed that the "media" version included quotes from several respected expert census journalists.