You can buy .eco domain name(s) from participating domain name retailers starting on April 25th, 2017.
Some retailers will begin selling .eco domain names starting on April 18th, 2017, but at higher “early access” pricing.
Some retailers allow you to submit an “expression of interest” for the .eco name(s) you want to purchase.
This could increase your chances of securing the name(s) you want.
Check with your domain name retailer of choice to see if they offer a pre-registration service or check out get.eco.