as well是"也"的意思你可以这样理解John plays football as well as David , if not better than him.John和David打球一样好,如果不比他更好的话
翻译一下就懂:John打球和David一样棒,如果不比他好的话。as well as 表示和……一样好as well=also
I agree with FishAlmighty.
fishAlmidhty的回答不错啊