For most people, it's annoying to painful.
The basic idea of 'Making Tax Digital' is that tax returns have to be submitted by specialist software. The option of using paper forms or, more usefully, the HMRC website which duplicates many of those but lets you fill them in online, would be over.
That it would happen was announced about ten years ago, but the wheels have run so slowly various people were wondering if it ever would. (Even when it comes to making laws, there are some which have been passed by Parliament and received Royal Assent but have never actually come into force.)
If you are unlucky enough to have business (escorting plus any other) income (not profit) of £90k a year, you should be registered for VAT. Even before the pain of having to charge it - which also means having to give VAT receipts with details you probably don't want to be handing out - you would have had to be dealing with MTD for the past few years.
The other change is that, as with VAT, people affected will have to submit something every quarter rather than just once a year. (The actual payment of tax will remain as one at the end of January the following tax year and, if the bill is high enough, a second one in July.)
The page linked to and the HMRC pages has some of the details: if your self-assessment income (not profit) from self-employment + property* is over £50k, it'll apply from April next year. If it's over £30k, it's likely to be from April 2027, and if it's over £20k, it's likely to be from April 2028.
At the moment people with a relevant income of under £20k won't have to deal with this. But if the limit doesn't change it will catch more people as time goes on, and if it does change, it might go down.
Once you're caught by this, you're stuck with it until your relevant income falls below the (currently) £20k for three consecutive years.
If you use someone like an accountant to fill in your forms, they should do this for you. They may well want to charge more for it.
At one point, various people I know had to use commercial software rather than the HMRC site to report income from a trust. The site didn't (and I think still doesn't) emulate that form. It cost about £20 a year, each, and the solution they chose was to change how they got the income so they wouldn't have to do that.
For income, the HMRC pages list a few free options:
1. Freeagent is only free if you have a NatWest group (so RBS, Ulster or Mettle as well as NatWest) business account. Having experience of NatWest, it's not one I'm going to ever want to use.
2. Academy of Energy is.. a pair of barely documented spreadsheets from something that talks about helping Russian energy suppliers a bit too much.
3. Self assessment direct / vat.direct takes a spreadsheet, as with the AoE, and uploads the details from it. Can't be less documented, so if I get caught by this, this is the one I will try first.
4. TaxNav, which doesn't seem to be available yet and whose site says 'try for free' rather than it being free.
Others may come along, because there are going to be plenty of people affected by this.
All this is about to affect companies as well, and there's an exemption for those who want to file in Welsh. I can see the temptation of this, and in starting a faith group with a religious reason for not using such electronic services (another exemption out there...) HMRC may not accept that someone using AW, with their own website, and using here really does have such a belief though!
* There are a few more things, but for people here, these are likely to be it.