It's a definite that you will only serve half of your sentence as long as you're not sentence to life, which you won't be. And then it's not definite that you can do your last three months on tag, but if you have a non violent or non sexual offence, and you get sentenced to under four years, then it's highly likely that you will be able to. If you're eligible they will send a letter to your cell / room, and you'll need to fill in the address you're intending on going to.
Like PP said, make sure you take your phone numbers written down. And pack well because if you pack light and then wait for a clothes parcel, you could be waiting a long time for the prison to process it.
When I worked in a prison you could take the following (they have a maximum number of items for each type of clothing;
1 Coat
12 items of upper body clothing (T-shirts / jumpers)
9 jeans / leggings ect
Unlimited underwear
Unlimited pajamas
One dressing gown
I'd also recommend taking a couple of towels, the prison ones aren't that great, they're very small, some stamps and envelopes (you get one prison letter per week, but you can take a few stamps in and some envelopes so you can write as soon as you get there if you intend to, and you can have stamps sent into you in the post), and take some money so that it goes straight onto your canteen money and then you don't have to wait for someone to send you any.
Your loved ones can email you now, and send money online. There's a website called emailaprisoner.
Do you know which prison you'll be sent to? Some have different rules, like no black coats (because the officers wear them), but I've worked in six and never seen any prison reception be particular strict about clothes. If definitely over pack though rather than under pack.
You'll spend the first few nights on the reception wing, where everyone will be new. Some will be regulars and will be asking you for vapes / food / clothes, just say no to begin with or they'll keep asking you. Obviously once you settle in and get to know people it's safe to give someone a stamp / chocolate bar or whatever without getting ambushed for all your possessions afterwards.
You'll be expected to work, or attend education whilst there. I'd avoid a job in the kitchens if I were you as they seem to work all the time. I'd opt for something like gardening just so that you're outside more, or in the gyms always a good job if there's one going. You get paid and you can spend it on your canteen and phone credit each week. You used to get your canteen sheet on a Sunday, fill it in by Tuesday and then get your canteen (shopping) on a Friday.
I've been to Styal before which is a women's prison, they live in big houses, have a gym, have a salon and can walk round outside for association. You'll be able to have weekly visits too.
I know prisons shit, there's no sugar coating it, but it won't be as bad as you think, you'll be ok and you'll come out of the other side safe and well. I hope you don't get a custodial sentence, or if you do I hope it's suspended, but whatever happens you'll be ok. We all make mistakes, it doesn't define us.
I hated working in a prison, I hated locking people in their cells at night and I hated seeing children cry leaving their daddy's after a visit. Prepare yourself for what you might see, there's a lot of self harm and unfortunately some suicide, but look after yourself, make a couple of good friends and just keep your head down and the time will fly by. There will be some idiot prison officers who think you're below them, but there will be so many nice, kind and understanding ones, and who cares what anyone thinks anyway.
Praying for a good outcome, and let me know if you have any more questions x