Annuals are usually sown in the spring - in my area I'd sow april or may. Perennials normally grown as annuals can be sown in the autumn, ie Sept or Oct.

Not much will grow at this time of year because there isn't enough warmth and light outside to support growth. And it's no use sowing them indoors, because there's even less light, and you'll get spindly leggy growth.

This is a generality, of course - there are, for example, some varieties of broad bean that can be sown now. But for annuals and most perennials, you'd be better waiting until spring, so you can get them into quick and strong growth.