I am a new user. Will any one please clarify when to use the ing form of the verb and when to use the infinitive form of the verb.

Thanks in Advance
The infinitive may be thought of as being an abstract form, a rough idea in the mind.

Adding -ing makes it a process which can commonly be better visualised,
or at least better understood.

Use the infinitive to talk about the verb itself, and its meaning,
also current wants, needs and desires.

Use the -ing form to talk about continuing processes and
potential or future wants and needs:

"I want to explain this to you clearly."
"You might be wanting a better explanation."
"I shall be thinking of this in my sleep."
"I wish I was laying on a beach." - or " ... I were ...", but that is archaic and formal.
"I am thinking."
"He is running."
"Is this guy rambling on?"
"Yes, he's running off at the mouth." - implies that he doesn't know what he is talking about.
Emotion: wink
This is one of those tricky things that native English speakers have difficulty explaining. I found a couple websites explaining the difference between the two, and I've included links to them on my blog here (see the links under "Infinitive"). Hope those help! Emotion: smile
 Logicman's reply was promoted to an answer.