Where I work, you're expected to use Outlook for emails and diary management, Excel for a range of things, Word less often; possibly PowerPoint. As with all Microsoft Office products, the exact requirements var. If you are the curious type you can quickly become proficient in a range of features which can set you apart. Make sure you mention them in applications, as people have very different views on what makes "advanced Excel skills" (many are not advanced at all - I speak from experience).
Apart from that you will use a range of job-specific packages, eg managing an online annual leave system, a finance system, a recruitment system, a costing system, a planning system, various databases and so on. Inputting data is usually a requirement, so attention to detail is essential. Being able to pull off standard reports may be necessary. If it's a more experienced role then you may be expected to analyse data from systems, and create bespoke reports - strong Excel skills can help hugely here.
I'd expect you to understand a range of local and corporate processes, and be able to advise other people on them. You may be purchasing goods and services and booking travel for others. You might be submitting their expenses too. More senior roles may have to help planning travel, and coordinate with diary management for senior staff.
Minute-taking is an under-rated skill and very transferable, especially if you are good at assessing the core message so that the minutes are concise and to the point, not verbatim.
I'd say an ability to keep things confidential is incredibly valuable. Both staff and managers need to be able to trust you. In these roles you often come across info before it's shared with all staff, and you don't want to get a reputation as the local gossip!
Best part - getting thanks for helping people.
Worst part - being taken for granted it's in the job description