If you arrive at Schiphol Airport Amsterdam, the railway station is located below the airport. You can take the Intercity Direct to Rotterdam Central Station (supplement might be necessary), so make sure you buy the correct ticket at the ticket office. At Rotterdam CS you have to switch trains to Vlissingen.
The other possibility is to take the train to Leiden Central Station and switch trains to Vlissingen.
Check the website of the national railway services for a travel planner, up to date travel information and train tickets.The price of a train ticket from Amsterdam to Vlissingen (one-way) is approximately €25. The trip by train takes approximately 2,5-3 hours.
This information is subject to change