What is the difference between a visa electron debit card and a standard visa debit card ?

A visa electron card is usually issued to a person under the age of eighteen. It isn't a cheque guarantee card so if you want to draw out money via your local post office you will be unable to do so, also though more and more shops now accept an electron card some still don't and you have the fuss of finding this out every time you go in a shop whereas a standard visa/debit card will be accepted in virtually all shops who accept a card for payment.
standard visa is a credit card and lets you spend what you have not got.
Electron isn't taken at all retail outlets where as normal debit cards usually are. So watch out for that one.
The main difference is that a Visa Electron card always needs to connect to the issuing bank to authorise the transaction. That means that you wouldn't be able to use a Visa Electron to order goods by mail order, for example. All transactions must be authorised electronically at the time of purchase, e.g. in a shop with a proper card processing terminal, or at a cashpoint (ATM). This means that the money is debited from your account immediately, unlike other credit / debit cards which can take up to a couple of days to "clear".

For this reason, there is no danger of you accidently overspending on your account, as the balance of your account is checked with each transaction. This is why VISA electron cards are often issue to young people / children as a first debit card.

With a regular Visa Debit card, the transaction is always guaranteed. Often, these cards double up as a cheque guarantee card.

Both take the money straight from your current (checking) account and are neither are "credit" cards.