Ruth Stout said you
should lay the mulch down first, then pull it away in spots to plant your seeds, so that they can get sun as soon as they sprout. Don't cover your desired seeds with mulch or you will stop them from growing, just like the weeds. Stout expressed irritation that people said, wrongly, that she said you should plant your seeds and then mulch over them.
If the soil is full of weed seeds and you are planning to direct seed all your vegetables, you might have to do something more to control weeds the first year. An example would be to smooth the soil surface, lay clear plastic over it, let a lot of weeds sprout, then remove the plastic and gently pull all the weeds without stirring up soil from below. After this, if you plant you vegetable seeds there should be less weed seeds than before. Another way is to smooth the soil, lay black plastic over it for a month or few months until the weeds below are all killed, then remove the plastic and plant without disturbing the soil much.
Another popular method is to mulch over the whole area with something that decomposes, but weeds really can't get through, like
cardboard or thick layers of newspaper.
Water it well, then stab holes in specific places and plant your seeds. You can mulch over the top of the paper or cardboard with other natural mulch. It will all decompose down and then next year natural mulch alone might be
enough to control weeds.