If you'll forgive the flippancy, it's getting up and thinking just before you walk into work 'OK, time to come across as something resembling a vaguely functioning human being'.
When you're sitting at your desk and people are thundering into your office and instead of yelling 'fuck off fuck off fuck off fuck off' you put your best smile on and say 'Hello - what can I do for you?' as responding to their query about something work related is a safe subject you can deal with. Except if they are just being friendly and asking how your weekend was, you're thinking 'What? Why? What's it got to do with you? Why are you telling me about your weekend? Go away? I don't care'. Then you have to remind yourself talking about your weekend is what people do. 'It was very peaceful, thanks. Yours sounds lovely....have you been there before?' because they can carry on talking about it and you don't have to share your Sunday spent cataloguing every houseplant you own and their lifecycle and leaf pattern stalk by stalk' (figuratively speaking, going into excessive detail about any subject would substitute for the description of houseplants).
It's when you are aware that you're repeatedly tapping and wiggling your foot because you are stressed, so you try and stop to avoid making the people who declare themselves to have misophonia wanting to hit you, so you try to silently move your hand around instead where it can't be seen, as you know that also irritates people.
It's when you might make a joke that if anybody wants you, you'll be under your desk rocking, they laugh, but in truth, that's actually your 2nd most desired outcome after getting up, running out the door and never, ever coming back but you know you need the money and therefore you have to let them think you're fine. with the mess, the constant noise and distraction.
It's when you really want to talk about your interests, but also know that this can result in a deluge of information about them that people don't tend to want, so you hold back even when they're talking about the same subjects - and worst of all, what they're saying is WRONG. So you have to walk away and avoid them as much as possible in future because you really, really want to put them straight but really, really, really need this job and getting into an argument about Star Trek TOS isn't really going to help you be popular in the office when you're coming to the end of your Probationary Period.
It's also when somebody says 'Oh, you are so good with x person who only ever wants to talk about their dog' and you smile, but you're thinking 'I'd far rather being talking with them about dogs all day than ever have to sit through a 20 lunchbreak with you going on about Love Island/children/etc. Well, actually, I'd rather be with dogs all day than have to put up with people at all because at least you know where you are with animals, they don't lie to you like humans do. But dogs don't need IT systems/bank accounts/housing advice, so I'm stuck with them if I want to be able to afford food'.
It's all those things you may try to do that you're doing deliberately to come across as not weird/dislikeable/difficult/annoying and it's all those things that you try to keep control over and not do because you've learned that people see to find them really annoying, distracting, irritating or outright get angry with you for doing.