I've heard friends say they were riding the clutch which led to wearing down the transmission, but what does it exactly mean??

Continually "riding" the clutch (letting it in or out very slowly such that the it is only partially engaged) wears down the clutch surface. As it wears down, the amount of friction it can generate decreases and the clutch may start to slip while engaged or have trouble engaging.
Your transmission is connected to your engine by the clutch plate and the flywheel, think of it like two plates being pushed together.
Here is a nice article explaining clutches and transmissions.
HowStuffWorks "Fly Wheels, Clutch Plates and Friction"

The first thing my father did to teach me to drive a "standard" was for me to put the car in first (with the clutch pedal to the floor) and the e-brake pulled all the way up. Then he told me to gradually let the clutch pedal up until I made the car stall out. By doing this I learned......

1. How the car felt approaching it's "engagement point", reaching it and beyond. Thus learning the warning signs and consequences.

2. Where exactly the "engagement point" is in relation to pedal height off the floor. Most often pressing the clutch completely to the floor is not necessary.

3. Got the nasty business of my first stall out of the way so I could concentrate on learning the craft.


So no worries, just jump in the water and tread. You'll get the hang of it we have all been in your shoes before.

P.S. On a hill I have found that the e-brake is your one true friend.

Best of luck.