We live in 21st century–each and every secretary works with computer. A good applicant for this job should have at least some knowledge of MS Office (or similar software they typically use in your country), including MS Outlook.
You should backup your knowledge with some experience, explaining them that you have worked with the software for some time. And you should also emphasize your effort to improve on your computer skills.
I can work with both MS Word and MS Excel, and also with MS PowerPoint. Actually, I have been working with these programs for the past five years. In MS Excel I can create charts and work with simple functions. In MS Word I can do pretty much everything the program offers.
When preparing reports in my last job, I worked with MS Office on a daily basis. On the top of that, I am very skilled with MS Outlook. I try new things with the software, trying to improve my knowledge of the functionality it offers.
Practical test in an interview
Some HR managers will test both your skills and trustworthiness with a simple exercise. There will give you a sheet of paper with some text that includes headings, bullets, and other text-formatting, and they will ask you retype the text to MS Word, with the correct formatting. They may even ask you to do some simple calculations, or prepare a graph, in MS Excel.
As you work on the task, they are observing how quickly you type, how quickly you work with the programs, etc.
The practical test can come, and you should have this option on your mind. Try to not overrate your skills with office software. Tell less, and surprise them with the level of your skills in a practical test–if it comes. Show them that they can trust you, that you are humble, but can work hard. Interviewers love job applicants with this attitude.