The numbers refer to the viscosity of the oil. The number preceded by W is the viscosity during the winter … the lower the number the easier it "runs" or "pours". A lower viscosity means easier cranking when starting in winter, and it also flows more easily to coat critical components more quickly.
5w30 >10w30 in the winter.
I run 5w30 all year though as that's what is recommended.
1994 DC4 LS-VTEC 5spd Championship White [Recycled]
1996 DC4 RS 5spd Milano Red B18B1
2006 DC5 Type-S 6spd Vivid Blue Pearl. K20Z1