New allotment

Firstly, welcome to the site and congrats on your new lotty 

Secondly, please could you edit your forum profile (click your username) to show your general location as this can affect the answers you get to questions 

This chart gives you some idea of what can be sown now.  You should also be able to get plants in garden centres if you're too late to sow many things.  Just make sure that you don't buy brassicas (cabbages etc) from a car boot or amateur gardener (minimises the risk of importing disease).

http://www.allotment-garden.org/vegetable/general/sowing-harvest-vegetable-chart.php

There have been a lot of threads in the last few days about what can be sown etc now.  Here is just one by way of introduction:
http://chat.allotment-garden.org/index.php?topic=79664

Info on what you should or shouldn't be doing is too wide to hazard much of a guess at ...