Welcome to the site, feel free to pop back into the welcome forum to introduce yourself
http://www.allotment-garden.org/vegetable/crop-rotation/index.phpThis is a link to various information on this site about rotating your crops.
For crops which you grow every year (as opposed to permanently), crop rotation means growing a crop in a different part of the plot each season, so that you don't end up in the same place more often than every 3 / 4 / 5 / 6 years - according to space and preference.
The rationale behind rotation is to prevent a build-up of pests and diseases in the same place, also to ensure that the soil does not get too depleted by plants constantly using the same range of nutrients - if you rotate plant families, you also rotate the needs of the soil.
Some people will have great crops by not rotating, e.g. beans, and some people argue that the size of a small allotment isn't big enough to prevent pests and diseases being transferred from one area to another, but if only for the soil nutrients reason I personally do advocate rotation.
P.S. You've learnt the hard way that if you ask 3 gardeners a question you'll get 5 different answers
Edit: sorry, just realised I haven't actually answered your particular question. I think within the same summer season is OK (unless you've had pests or diseases on the first crop) but people tend to advise not growing in both winter and summer seasons, if I recall correctly e.g. brassicas. But I think people will definitely disagree more on this particular point.