Is there an easy way to spot a 'gerund'

[lespol]

Hi all,
I'm new to this forum, but from what I've seen, I'm going to love it. I would like to ask if someone could tell me a 'foolproof' way of spotting a gerund. I have to do some for a test, and I can't be sure. This is urgent, so if you could help me ASAP, I would be very grateful.
Thanx in advance,
Les

[Tdol]

If it comes after the verb 'be' or is modifying a noun, it's not a gerund. If it is the subject or a verb, comes after a main verb, or after a preposition, it is.

[lespol]

Dear Tdol,
Thank you again. I don't understand 'modifying a noun' or 'If it is the subject or a verb, comes after a main verb, or after a preposition, it is. I can't do these things honestly. Could I have an example of each one when you have a moment to spare please. I have decided to completely re-study English for fun and although I know my language, I don't always understand why.
Thank you so much again,
Les