"How long is my registration valid?"
You can decide on a registration period of anywhere between one and ten years.
Before the Shared Registration System (SRS), you didn't have many options. An initial registration was for a period of two years, and you could only renew for one year periods thereafter. And, of course, it was more expensive.
Now it is all very flexible. You can renew your domain at any time for any number of years so long as the total period does not exceed 10 years. So you can register a domain name today for a period of one year, and come back to renew it next week for an additional nine years, if you so desire.