Audio Splitter for Dell Inspiron 11 3000

Dell laptops come with one single audio / mic. port. I need to use this:

a/ with a headset / mic. combo for making private calls via say Skype;
b/ with a stereo head set to listen in private to stereo recordings (with the internal speakers muted); and
c/ with a Behringer / iMic device for analogue stereo input from a record deck or tape recorder in stereo for Audicty to digitise.

However the splitter cable with one male plug / two female sockets come in a variety of types:

1/ the male plug can have 3 exposed contacts or 4 exposed contacts on the stem

2/ the two female sockets can be

a / both for stereo audio output for a stereo headset OR
b/ one for mono audio output with the other for mic. input for combination headset / mic. units OR
c/ both for analogue input for connecting to a digitising unit such as a Behringer or iMic

The issue is that obviously its important to use the correct male plug - but which type; and secondly the various types of splitter cables appear to be identical but have totally different functions and wiring?

Dell doesn't say what the sole audio port is for; neither does it say which type(s) of splitter to use.

The generic splitters on eBay and Amazion all look alike and the descriptions rarely say exactly how they are wired and what they for.

BTW I have no problems with my Toshiba Qosmio nor my Acer AO 532h - because they both have stereo input AND output audio ports.

Thank you.