Wales go into the Manchester tournament on the back of a Six Nations Grand Slam and there are high hopes.
They face Ireland in their first match on Tuesday and Williams, who joins Cardiff Blues academy this summer, insists the Six Nations victory counts for little.
Williams said: “It was a big boost for us as a team to win the Six Nations and a Grand Slam but this is a different tournament and we just have to focus on the first game against Ireland.
“We’re champions of the Six Nations and that gives us confidence but all the other teams will up their game, it’s a totally different tournament.
“It’s a massive game for us and it’s important to get momentum going into the second game.”
Following Tuesday’s clash with Ireland, Wales will then take on Georgia and New Zealand in the group stages.
After the commencement of the global gathering, Williams will move south to Cardiff and he is relishing his involvement in regional rugby.
He added: “With RGC securing promotion to the Premiership it was a tough decision but I wanted a different pathway and to get into the regional set-up.
“Signing for the Blues will be great for my development.”