Again quoting that I am currently very new to RCs and I first want to gather all possible technical knowledge i can, no matter how elementary it may sound.
Here are my questions:
1. For an electric propeller what does this kind 10"x 6" of nomenclature mean? I can understand what 10" would mean buy what does 6" mean?
2.What Electric Propeller, Sport Propeller, Pylon Propeller and Slow Flyer Propeller?

Regards
Vaibhav Sharma

[1] The second number in prop specification is pitch. 

http://www.rcindia.org/rc-general-topics/propeller-what-do-we-understand/ has more details than you need for a while

You should use the search option to find such threads

[2] This thread has a basic information on the difference between various types of props.  The main difference is the rpm each is designed to run at.

http://www.rcgroups.com/forums/showthread.php?t=846413

If I am trying to build a model in which i have very low constraints of voltage and current. Which means that I shall not be able to get a motor of very good RPM. I intend to make a boat kind of a structure which works by pushing/pulling air through propellers. What kind of props do you suggest? And what would be the minimum RPM i would require.
The max voltage i get is 6V
The max current i get is 400mA
The weight of the structure would be 250gms
I will be using a prop of dia less than 8 but I am not able to decide on the pitch and the kind of prop, slow, fast, sport. How many blades would be preferred, 2 or 3?

Regards
Vaibhav

With those strict parameters, wonder if you should be looking at the the micro-flight motors like these.

http://www.microflight.com/Online-Catalog/Motors/7mm-3-3-Ohm-Coreless-Motor

Please read through http://www.microflight.com/Online-Catalog , you will find lots of stuff that applies to your requirements.