OK, here's a try at a neutral explanation of "The Budget" in general, if that's what you meant. You can get a million opinions on "The 2024 Budget" elsewhere in the thread. 😉
The Budget sets out how the (any) government plans to finance the major elements of its political programme. So if they have said they want to put more money into the NHS, the Chancellor of the Exchequer (CX) will say how much that is, say an extra £20 billion, and then explain where that money is to come from, which can be a combination of borrowing, taxes, or cutting spending elsewhere.
Sometimes CX will also cut specific taxes while raising others, if they want to encourage — or at least not discourage — some behaviours more than others. Or they might not decrease/increase tax rates directly, but instead raise/lower the amount of money you have to be earning/paying before those taxes kick in. As well as taxes, the Budget may also adjust benefits and other financial rules. For example, yesterday it was announced that the minimum wage will go up by about 7%. That's not a spending decision as such, but it's a number that the Government sets by law.
The extra money being spent tends to overlap with things that other ministers have already talked about, and often takes a while to go through the system. On the other hand, tax changes sometimes come in quite quickly. (But then again, some take quite a while. Air Passenger Duty — a tax you pay when you take a flight from a UK airport — will change a bit in April 2025 because of a decision taken by the outgoing Conservative government which is still waiting to take effect, and again in April 2026 because of an announcement that Rachel Reeves made yesterday.)