Amos, 21 on Thursday, was preferred to the experienced Alex Cuthbert and will win his fifth cap at Twickenham on Saturday.
"We feel he can play on the wing or at fullback where he gives us a left-foot option," Wales coach Warren Gatland said.
"In training, I couldn't believe how good his footwork was. It took me by surprise."
Amos, who was born in Stockport, England and moved to Wales as a four-year-old, has just finished his second year of medical studies at Cardiff University.
"World Cups are the biggest thing in sport and one at home might not come around again in my career," he said.
"I have been in and around the squad for a couple of years. It's often tough sitting on the sideline and being travelling reserve, watching the boys go out there."
Having scored a try in Wales's opening 54-9 win over Uruguay, Amos gets another chance on Saturday in a massive game against England whose quicksilver wingers Jonny May and Anthony Watson will pose a huge threat.
"England are a very potent attacking force," Wales defence coach Shaun Edwards said.
"They have electric backs and play expansive rugby. It will be a huge challenge for us."
(Reporting by Ed Osmond; editing by Justin Palmer)
