Just to be clear, it says for the gauge swatch you should cast on 25 sts?
The ribbing pattern would be: row 1: p3, k1; row 2 knit the knits and purl the purls (as they appear on this side).
Do the instructions tell you to slip a stitch?
Can you link to your pattern, that is generally quite helpful.
You can't knit the left sock first. Ever.