Hi,
Depends on the plant.
Peas and broad beans can be seeded outside as of 25th of February (here).
Here Icy Saints are on the 10th/11th of May so we're free to plant tomato plants (beans, and all) outside after 12th of May.
Of course, we always challenge ourselves and try to do some on 15th of April ... Just to cry out loud some years .
You would seed the tomato plants in a cold greenhouse by 1st of March, let grow inside the greenhouse, later separate to individual pots... Lots of TLC.
As for fig seedlings, believe me or not but I have a toothpick sized one that is making its life in the garden with just an upside down pot over it ( small 80liters trashcan technique ... LOL ). I took a pic yesterday. I'll post it later ... Sometimes doing nothing is best ...