The Australian said that the new car felt similar to the 2012 RB8 that won both the drivers' and constructors' championships, but he added that the team had areas to work on before testing resumes on Wednesday morning.
"The car was very understeery today, so we need to improve that tonight and get it a little more responsive," Webber told reporters at Jerez.
"Obviously this was the first day at school. We're not having a grand prix tomorrow, thank God, so we'll work hard, as will everybody else.
"The car's not massively different. The last few years we've had regulation changes, but this year it feels pretty similar.
"We've got some front wing stuff going on, but I felt pretty comfortable pretty quickly."
Webber added that the combination of the new 2013-spec Pirelli tyres and the rough Jerez track surface could be exaggerating any car traits.
"The tyres are going away quite a bit," he said. "If you see a car on fresh tyres the performance is quite nice, if you see one on older tyres it doesn't look very nice.
"The naked eye can even see the problems. The tyres are struggling to do quite a few laps, and you see the times in the 1m22s and 1m23s.
"But this track is always hard on tyres. You can always scare yourself here and then get to other places and it's OK."