It means "not only...but also...", or "... and..." 他的汉字写得又好又快。He writes Chinese characters not only fast but also well. He writes Chinese characters fast and well. 那得东西又便宜又好。Those goods are not only cheap but also good. Those goods are cheap and good.

“又...又”的意思是“不仅...,而且...”，连接两个并列成分。 “他的汉字写得又好又快”，意思是他的汉字写得不仅好，而且快。 “那的（！不是"得"）东西又便宜又好”，意思是那的东西不仅便宜，而且好。