To quote the U.S. National Archives site, "The National Archives web site has very few actual records online. The National Archives has a very large amount of records that are useful for genealogy, but most of these records are not online." Some of the resources for genealogists are listed on the "Start Your Genealogy Research" page. However, I notice that the links on this page are out of date. I suggest that you copy the names of the individual source entries and search for the records on Google. In some cases, the Google search will take you directly to the correct page at the National Archives.
The newest addition is the Online Public Access (OPA) catalog. According to the website, the older Archival Research Catalog (ARC) will be replaced this summer (2013). However, the Access to Archival Databases (AAD) is still available. An online public access catalog is a computerized database of the bibliographic holdings of the library. Initially, such systems were roughly equivalent to the old paper-based card catalogs, but they are much more sophisticated today. One of the best known of these catalogs is WorldCat.org.
In using the OPA, I was taken immediately to the online images of the Dawes Rolls. However, the other searches did not give me an indication that the actual records were digitized and online. It really helps if you know what you are looking for in the first place. But if not, the searches give you a lot of documents that might help. As their statement above indicates, there are only a small percentage that are actually online. Even with the revamped search engine, research in the National Archives is not for the faint of heart or inexperienced.
You can also use the search box on the National Archives startup page. For example, if you were searching for the Dawes Rolls (the Final Rolls of the Citizens and Freedmen of the Five Civilized Tribes in Indian Territory), you will find the Dawes Rolls either with a search through the National Archives search box or on Google. In either case, the page has a detailed explanation about how to use the records.
Creating an Online Public Access (OPA) catalog for the National Archives is a big step towards making the records available to the public. It is interesting to compare what is going on in the Washington rather than the city of Washington, D.C. with digitized records. The Washington State Archives has a Digital Archives website. So far, the State of Washington has digitally preserved over 136 million documents with over 37 million of those documents completely searchable online. They are adding approximately a half a million documents a month. Although the National Archives is making an effort to enlist third-party companies and organizations to digitize the records, it is not nearly so involved in making digitized records available to the public. The Digitization Services Branch at the National Archives and Records Administration (NARA) makes a wide variety of products for internal NARA customers but not for the general public. The OPA prototype currently provides access to nearly one million digitized records which are kept in the Electronic Records Archives (ERA). Possibly, national security, personal privacy, and law enforcement information issues are limiting the number of documents available online to the public, because as of January 2012, ERA supports over 131 TB of electronic records, including records from the George W. Bush White House, many Federal agencies, and Congress.
Considering that FamilySearch.org and Ancestry.com can digitize and make available millions of records a week does not make the National Archive efforts seem so impressive. But, of course, both these organizations do not have to deal directly with either Congress or the President.
The scope of available documents from the National Archives is extremely impressive, but for the time being, until more are made available online, researchers will still have to make the trek to the National Archives or one of its Branches.