You use introverted Sensing or Si when you're reviewing the past. When you're remembering the songs that were playing and the dress you were wearing at prom. When you are right back on your grandfather's lap as he tells you a good night story. When you know exactly who first brought that Christmas tree ornament into the house and how it looked on the tree. When your colleagues ask you how to do the inventory, and you show them how you did it last year. And when they tell you the results you recall exactly what the difference is.
For people with Si as their dominant function, they cannot not remember. Virtually anything you say will trigger a catalog of details and images of what happened before, and how it influences the now. Sometimes even how it could be carried into the future, to carry on the tradition.
Expats preparing for an assignment using Si are likely to mentally review everything they already know about the country they're moving to. Things they may have read in the news, heard on TV, or have been told by friends and family. Since the news may be one-sided, it may help to establish another set of references by learning about the country from different sources, like expat blogs or travel guides. You might also want to observe and learn from an expat who has successfully relocated and could serve as a role model to emulate.
If Si is in different positions in your type dynamics, below is an overview pieced together with only a few items taken from Understanding Yourself and Others, An Introduction to the Personality Type Code, by Linda V. Berens and Dario Nardi. Let me say this again to be very clear: the description of how Si can be expressed in the different positions is not exhaustive and only meant to give you an overview. I would love to have you comment below how it shows up for you.
If you'd like to practice your Si skills, take some time to travel back in time. If you need help, you can watch a family movie, thumb through the old photo albums, or sit with your elders and listen to their stories. Try to remember where you were exactly at any given time, what the mood was like, what the newspaper headlines were that day or week or month.
Repeat the exercise in a month and try to remember at least the same amount of details about the same event.