Help picking out guitar strings? (electric, SG)?

The gauge size is the size of the strings in millimeters. .09, .10 and so on. If your just starting out I wouldn't worry about pure nickel or anything speciallty string. If you have an SG then it's set up for .09 gauge strings. I prefer GHS Boomers in .09 gauge, but thats just my preferrence. Ernie Ball Super Slinky's are decent strings too.