Q.starting a plant from seeds
Every time I start something from a seed it grows tall and skinny and then falls over and dies. Tomato plant, pepper, zinnia, sunflower–it doesn’t seem to matter what. I use starter soil and sunlight, so they come up fine….what can I do?

Make sure you purchase and use 'soilless mix' for starting seeds, not a potting mix.
Soilless mix is light so that the seeds can grow.
Most seeds need a warm environment to germinate.
Tall and leggy seedlings are generally due to low light, a grow light is the best way to grow good seedlings indoors.
Provide some air flow when the seedlings have emerged. This helps keep fungus away and grows strong roots and plants.
I even brush my hands gently across the seedlings several times a day.
Make sure the moisture is maintained evenly on seedlings. If they are soggy or allowed to dry out--this is certain issues or death of the seedlings.
I would encourage you to try again, but maybe keep it simple for the first time.
Zinnia and Sunflower Seeds can be easily directly sown into the garden, no need to start indoors.
Pepper seeds can be tough, even for a seasoned gardener.
Tomato seeds are a great one to start with!
Here are some links to help you get started.
https://www.gardeningknowhow.com/garden-how-to/seeds/soilless-seed-mix-info.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/starting-indoors-direct-sowing.htm
https://www.gardeningknowhow.com/garden-how-to/seeds/when-to-start-seeds.htm
https://www.gardeningknowhow.com/garden-how-to/seeds/preventing-white-fluffy-fungus-on-seed-starting-soil.htm
https://www.gardeningknowhow.com/garden-how-to/seeds/what-is-damping-off.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-from-seed.htm