When the cutting phase ends, you move into Calorie intake equal to energy expenditure, resulting in stable weight.Full definition →, and the central change is simple to state: you stop running a constant deficit. You are allowed more food now, and you get to spread it across the things you want to eat. For some people that is genuinely the easy part. For others it is the most slippery stretch of the whole program, so it pays to go in with your eyes open rather than treating the end of the cut as the finish.
The change itself
Through the program you ran a deliberate gap between what you ate and what you burned. Maintenance removes that gap on purpose. The job changes from losing weight to staying where you are, which means finding the calorie number that keeps your weight level and eating to it. That number is higher than your deficit number, and a little above your old losing intake, so in practice it means adding food back: more of the proteins you relied on, a bit more on the plate, the occasional thing you kept out. It sounds like the reward at the end, and for some people it is exactly that.
Why it can get slippery
Here is what tends to happen. After two or three months on a narrow list, you will long for the things you left out: bread, pasta, potatoes, fruit, chocolate, maybe a glass of wine. So you begin to bring them back, which is reasonable in itself. The catch is that these are usually the same foods tied to your old way of eating, and bringing them back can switch those old patterns on again. If that starts to happen, the move is to deal with it early, while it is small, rather than letting it build over weeks. There is separate content for working through that part when you reach it.
The straightforward version
There are really two versions of this transition. In the first, you have had your fill of those foods and do not feel much pull back to them, and the tracking never bothered you across the ninety days. If that is you, maintenance is mostly arithmetic. You work out the number that keeps you level, add a bit more to your daily intake, more chicken, more eggs, the occasional piece of fruit, and carry on much as you have been, only with a higher ceiling. It runs on the same habits that got you here.
The version that takes real skill
The more common version is that you want normal food back. You want to eat at a restaurant, have a bowl of pasta now and then, eat the way the people around you eat. That is a fair thing to want, and it is also the part that takes genuine practice, because those foods are calorie-dense and hard to stop at a sensible amount. Maintenance is its own phase with its own demands, and like the deficit before it, it can take more than one attempt to settle into. Going in expecting that, rather than expecting the effort to switch off the day the cut ends, is most of what makes it work.