Can I tether data from my Ascend Y Straight Talk phone to my Samsung Galaxy Tablet?
call your provider and they will guide you
If I'm not wrong Ascend Y operates in an Android OS. So, if you go under setting > wireless and connection settings, probably it's an option for tethering (depending on the model of the mobile and version of android).
If there is no option, check for an android app:
If your mobile os is not an android, than check for an app (created for your mobile os), that can give tethering options to your mobile.
If you are sure that the carrier will not overcharge you for tethering,then it would be safe to go with.Many carriers have tethering plans which if you subscribe to will get the full benefit.