Once you are in Finland you want to either go directly to the check-in at the airport or use the automated check-in. The automated check-in service works in multiple languages including English and is easy to learn and use. Have your passport and a printed version of your flight booking at hand.
To save time, while you are still at home, print out your boarding pass online before coming to the airport.
The other option is to check in at the airport and have a boarding pass ready to go through security. At the Helsinki-Vantaa airport last time we flew from Helsinki to Copenhagen it took about 20-45 minutes to complete the security check. At security make sure any liquids, gels, etc. are in a clear plastic bag.
Ryanair for example has a rule that the carry-on must not exceed 10 kilos (22 pounds) and luggage dimensions must be within 55 cm x 40 cm 20 cm, or else you pay for excess luggage.
When I flew from Phoenix, U.S.A. via Germany to Finland in January my airline carrier told me that 50 pounds (22.6 kilos) per checked in bag was the maximum weight, and the dimensions could not exceed 63 inches (160 centimeters). You'll have to pay cash for transporting oversized luggage!
You can buy an airline ticket with a major credit card or debit it from a Finnish bank account.
Each person has a place of residence and nationality. For air travel to Finland start by bringing an updated passport. For more questions use the Ryanair website for other type of travel documentation to bring along.
Yes, usually you can make changes to the date or persons specified in your tickets up to the last minute. For example, Ryanair allows changes to be made up to 4 hours before the flight leaves.
Since Ryanair provides service to Finland, they have a very concise page with questions and answers related to air travel to Finland on their website.