It all depends on what you are wanting to grow. There are lots of veg and flower seeds you can start off about now, although I see you're from West Yorkshire, so you might be advised to wait a week or two.
Seed packets will tell you when/how to raise the seeds.

It says you should on the packet but I start my fench marigolds in a cold gh.
maybe worth puttin on a bench though and cover at night if temperatures drop.
I started some dahlia tubers in pots too
tomatoes and peppers I put in a propagator in the gh

grass????????