please tell me are gherkins good for you and if so why? What do they contain etc. If bad for you please let me know that too.
Basically NO - they are made from cucumbers and SALT.
The nutritional information for one brand of Gherkins is here:
As you can see 3 of them are only 40 calories, but 150 mg of Sodium. They do contain some fiber - however you can get that without the sodium by eating the RAW cucumber.