Tomatoes and peppers are two things difficult to grow from seed. When to start depends on the plant type.
Melons are fun to grow because they start well I doors, transplant easily, then grow like gangbusters. However, they require both male and female to bear fruit so enough must be grown to hopefully get at least one of each.
Some seeds need special starts like scraping the hull, or sprouting between moist paper towels.
Therr are helpful videos, but not always specific to what someone needs. I wanted help to grow kiwi fruit, but all I found was in Europe, except one using plant starts instead of seeds.
I hope you have good luck with your garden. It is so rewarding when they go well.
I have had good luck with using yogurt containers for indoor starts.
Sunflowers are fun, because they get eight inches tall a couple of days after they sprout. The very big kind produce such a great batch of yummy seeds.
Potatoes are fun because it is like finding buried treasure. You see the plants growing, and one day you dig it up, and there’s a pile of potatoes hiding there.
From seed to fruit, tomatoes require constant tender loving care. Bugs, weather, watering, it is like raising a child. If it goes well, it is great, but even birds will sometimes peck at tomatoes for the seeds, or bugs which happen to be on them.
A good friend to gardens is a praying mantis. They eat every kind of bug besides aphids, but they are friendly to people. They are not plant eaters at all.