To link your Android phone with FreeTextSMS.net web application, you should login same account in both sides.
If you have not registered account, you can register one with your email name.
You should click a link in notification email of registration to make valid your account.
You can use your register information to login in FreeTextSMS.net/web application.
After login in freetextsms.net/web web application, you can scan 2D bar code on the page to login in your Android application. Hence, your Android phone will be paired with web application and you can enjoy all you Android SMS functions on your browser.