I am confused about what the square on the label of a skein of yarn means. It has numbers such as 10x10 cm on one side, 18 R on another side and 14 m on a third side. The recommended needle size is 6-7. Can anyone explain it in simple terms?
10 cm is the equivalent of 4", and it sounds like you've got a German yarn. The needles are mm so they would be US size 10 (6mm) and a little larger than a 10½ (7mm). The m would be stitches, the R is rows so the gauge is 14 sts and 18 rows over 4". It sounds like a heavy worsted/aran or bulky yarn.
Occasionally you'll find patterns online that are written with needle sizes in mm or UK sizes rather than American needle sizes. It's the same with yarn information. Here's a chart that may help you. I have a Susan Bates metal knitting gauge ruler with holes in it for determining needle sizes. I noticed that both the American sizes and mm sizes are on it. Hope this helps when you're converting from metric. Some of the knitting gauges also have mm sizes in the rulers. As a last resort, grab your better half's carpenter's retractable tape measure. It also has both.