Well draining soil, lots of light, cold winters and not super hot summers are what lavender like. They don't like soggy roots but do not like long dry periods. They get attacked by aphids so a little pest control is needed.
You need to cold stratify the seeds first. Put them in a baggy with a damp (not wet) and then in the fridge for sixish weeks. Keep and eye out for mold and open the bag once a week to refresh the air. Then put them in a seedling tray with some light drainable growing medium. Put in a sunny spot that's warm and keep the medium moist with a spray bottle. Keep this up until you see sprouts.
You can remove the seedlings from the growing tray once the get their first set of true leaves. The sprout leaves aren't technically real leaves. Sun harden the seedlings before putting outside for potting or in ground planting.
Good luck!