Congratulations milliezoe.
Has the allotment been used recently? If not you may need to clear the weeds.
get down there and meet other holders they are a mine of info.Find out if there is an allotment shop for cheaper gardening supplies.Is there an allotment association.
potatoes are a good crop to start off with they help to break up the ground. Can go in anytime around now. Get a book from the library , something simple on the lines of veg growing for beginners.
Don't be too ambitious in your first season, spuds, cabbage , peas , runner beans something like that, a few lettuce .
Organise a drum for water saves a lot of treking about.
Eventually you could have a little shed.
Have had an allotment for over 30 years , can't beat being down there very early am in the summer , with a flask of coffee , my brekkie in a paper bag , contemplating my navel before the world awakes.Total bliss. Sincere good luck and happy growing.