To answer all the issues you raise would require a book on US electrical wiring. Or several. And a copy of the Code.
The vast majority of outlets in residences in the US are attached to branch circuits that are rated at 15 Amps and 120 Volts. Current practice and code calls for outlets like these
This version is tamperproof, required in many jurisdictions. The non-tamperproof look similar, but the slots do not have internal baffles
You may see different styles, such as Decora, or decorator style, which are functionally identical to basic outlets, but have a rectangular face
20 Amp circuits generally require slightly different outlets (if you are going to draw the full 20 Amps or there is only one outlet on the line) like these
But you can also find the lower 15 Amp outlets on circuits that are properly wired for 20 amps. Obviously 15 Amp outlets are limited in use to 15 Amp appliances, even if they are on a 20 Amp line.
Certain locations, especially where there is a risk of moisture, such as bathrooms, require a ground fault interruper (GFI) type outlet
These also come in tamper resistant and 20 Amp versions and vary like the basic outlets.
All of the above are grounded outlets, required in almost every jurisdiction for new construction and renovations. Some older installations may have ungrounded outlets.
These generally cannot be used except as a direct replacement for an existing one, and even then setting up a properly grounded outlet is preferred and may be required.
All of the 120 Volt outlets require a hot wire (usually black or red) and a neutral wire (always white). Grounded outlets also require a ground wire (green or bare). Outlets can be always live or switched. Live outlets have the hot wire coming directly from circuit without interruption. Switched outlets have the hot wire going through one or more switches before reaching the outlet so that the power can be turned on or off.
All of the 15-20 amp outlets shown above are duplex, that is there are two receptacles for plugs on each. These almost always are bonded together by a strip of metal. When you wire to one, both are energized. This bonding strip can be broken off allowing each of the receptacles on the outlet to be powered separately. This is most often done to allow one receptacle to be always live and one to be switched. This also allows each receptacle to be on a separate branch circuit (for heavy power use).
Some residences use higher amperage outlets for large appliances, such as an electric stove or dryer, and the outlets vary base upon a number of factors. Examples can be seen in the chart linked in the question.
Similarly, some residences use 240 Volts for large appliances and wells, and the outlets also vary considerably, and can be seen on the linked chart.
This is a very brief summary of the type of outlets most commonly seen in US homes. The full range of outlet types and uses is beyond a simple summary. The range of possible switching and wiring configurations also is nearly infinite. But this site welcomes questions on any particular configuration or problem you may encounter, so ask away.
Best Answer
Sockets that can be used for both grounded and non-grounded 6A plugs are quite common in India. Other variants allow using grounded 6A and 16A plugs. Some examples are shown on the Digital Museum of Plugs and Sockets pageĀ http://fam-oud.nl/~plugsocket/OldBritish1.html (see images 8-13).
It seems likely that the images (a) and (b) show a socket that is designed for grounded (3-pin) and non-grounded (2-pin) 6 Amp / 240 Volt plugs. The lower two slots of the socket are Neutral (left) and Live/Hot (right). Together with the center top slot for grounding, they are meant for a 3-pin plug. The top two slots, at left and right of the larger ground slot are meant for a 2-pin plug.
The spacing of the L and N-pin of a a grounded 6A plug is 18.5 mm, whereas the spacing of the two pins of a non-grounded 6A plug is 16.6 mm. Unfortunately the photo is too vague to see whether the spacing of the top two slots is about 2 mm smaller than the spacing of the lower two slots.
The tolerances of Indian plugs and sockets are often quite large. It is often not too difficult to insert a 2-pin plug in the L and N slots meant for a 3-pin plug, which means that you can use both the top two slots (correctly) and the lower two. Using the lower two for a 2-pin plug is not really safe, because it is probably not possible to insert the plug completely. Note that in both cases the plug is inserted in a horizontal position.
The possibility two insert a plug in vertical position is remarkable. To my opinion it is a design fault. Usually the two slots at the left side are both connected to neutral and both slots at right to live/hot*. Insertion of a plug in vertical position is useless since both pins are connected to the same wire, either neutral or live. In both cases there is no potential difference.
Note that a connection to two hot poles may look comparable to split phase wiring which is commonly used in the U.S., but in the Indian situation the two live poles are identical = in phase, rather out of phase for split phase wiring.