Please can someone give me a SIMPLE but comprehensive explanation (or direct me where to get one) of the half and full bet rules.

Everywhere I look I am only able to find the same generic explanation which misses some of the intricacies, please see below.

‘If a player goes all in with a raise rather than a call, another special rule comes into play. There are two options in common use here: pot limit and no limit games always use what is called the full bet rule, while fixed limit or spread limit games use either the full bet rule or the half bet rule. The full bet rule states that if the amount of an all in raise does not equal the full amount of the previous raise, it does not constitute a "real" raise, and therefore does not reopen the betting action. The half bet rule states that if an all in raise is equal to or larger than half the bet being raised, it does constitute a raise and reopens the action.

For example, a player opens the betting round for $20, and the next player has a total stake of $25. He may raise to $25, declaring himself all in, but this does not constitute a "real" raise, in the following sense: if a third player now calls the $25, and the first player's turn to act comes up, he must now call the additional $5, but he does not have the right to reraise further.

The all in player's pseudo-raise was really just a call with some extra money, and the third player's call was just a call, so the initial opener's bet was simply called by both remaining players, closing the betting round (even though he must still equalize the money by putting in the additional $5). If the half bet rule were being used, and the all
in player had raised to $30 instead of $25,then that raise would count as a genuine raise and the first player would be entitled to reraise if he chose to (this would create a side pot for the amount of his reraise and the third player's call, if any).’

I just can’t seem to get my head around it……… HELP!!!!!

What you posted seems straightforward, what are we missing?

The all in player's pseudo-raise was really just a call with some extra money, and the third player's call was just a call, so the initial opener's bet was simply called by both remaining players

That seems to sum it up: unless the raise is large enough, it does not re-open action to the initial bettor/raiser.

I see your question.

A legal raise is double the previous bet or raise

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Here's a quiz I put together sometime ago. It also links/references the Mike O'malley article in CP that may help you out.

Betting

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unless its an all in

Normally, for an allin to be a legal raise that can re-raised, it has to be double the bet or previous raise.

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I think the key to this question is that the all-in that is below a raise has to cap the action.

For instance: UTG raises to 50, MP calls, Button calls all in for 60, blinds fold.

The action is not reopened for UTG, he can only call the $10 - same for MP.

However in this situation:

UTG raises to 50, MP calls all in for 60, button raises to 300 . . . .

is legal, because the action is open (MP calling 50 would not cap the action).

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Jason75: Ok, you check and the button bets 400. Now what?
Beavis68: You play poker.
Jason75: Darn, I was really hoping for canasta. Maybe Gin.

i meant like, if somebody has $100 and somebody bets $75 preflop, the person is able to push in for $25 more, however if he had $1000 he could not raise 75 more.