You can use
http://www.hyperdia.com
Hyperdia will give you a lot of results.
For each different train company you pay a separate fare for those segments.
You can buy a ticket at the entrance to each station. You insert the ticket to actually enter the station and insert the ticket again to exit the station. Each of the lines I indicated above has a seperate entrance and exit.
I have listed the fares above, you just push the button for the amount of fare you want. For example Maihama to ShinKiba is 150yen, walk up to the machine and press the 150yen button:
http://www.flickr.com/photos/richardharrod/4113115721/
Alternately you can purchase a PASMO (or Suica) card.
This is a transit debit card where you load funds onto the card and it is subtracted each time you use the trains (DisneyMonorail excluded). The card has an initial deposit of 500yen that you can refund later if you return the card. So if you buy the card for the first time, you might insert 2000yen and get 1500yen worth of credits.
However it would probably be late by the time you get back for the office to refund you the 500yen deposit, and maybe too early for the office to be open the next morning to refund your pasmo/suica card.
Therefore if you are only riding the trains back to HND just purchase tickets as you go, again the prices are laid out in my other posting.
I broke them down in my previous list.
Haneda Airport is listed a few ways on Hyperdia:
"HANEDA AIRPORT DOMESTIC TERMINAL" - Keikyu Railways Station serving both Terminal 1 & 2.
"HANEDA AIRPORT INTERNATIONAL TERMINAL" - Serving both Keikyu Railways and Tokyo Monorail. Separate stations but share the same name.
"HANEDA AIRPORT INTERNATIONAL BUILDING" - No longer in use.
"HANEDA AIRPORT TERMINAL 1"- Tokyo Monorail Station
"HANEDA AIRPORT TERMINAL 2"- Tokyo Monorail Station.
On the trains there are displays switching between Japanese and English.
So when you're on the train if the next station is SHINKIBA it will display "SHINKIBA" the displays are usually above the doors on the trains.
So get off at the indicated stations and follow the signs for the transfer (signs also posted in Japanese and English). For example, when transferring at ShinKiba follow the transfer signs to the "RINKAI LINE".