Some cruises do allow you to take alcohol on board.
I have just booked a P&O cruise and they allow 1 litre of spirits per person (or beer, champagne etc). Check the cruise paperwork or web site.
Note you can also buy "drinks" packages so check how much they are as over a full cruise it may be worth it.
I don't drink alcohol but do drink soft drinks (coke etc) so I bought a soft drinks package and it was great to be able to go up to any of the bars on the ship (about 20 of them) at any time of the day or evening and get a fresh cold drink.
You may find an alcohol package worth it.
I did my first cruise last year and had many basic questions so if you have any questions just ask here and we will try and help.
I found the Cruise Critic web site helpful as they review every ship and every cruise and every port so you can find out a lot before you go.
They also have forums where you can ask questions.
https://www.cruisecritic.co.uk/