There are lots of websites and videos which show you how to start your seeds inside, but the question is “What do you do after the seeds have germinated?”
I have started seeds indoors for many years and have pretty good success. The problem I always have is that the plants get tall and have weak stems and don’t do as well as I’d like when they go outside.
Mary Ann Fink has given me a number of suggestions which should help.
Pinch the end of the plants when they get two or three sets of true leaves. This will encourage the plant to send out lateral shoots and be bushier instead of just tall.
Use an oscillating fan to push the plants back and forth. This will encourage them to make their stems sturdier.
Finally, give them a pat on their tops. This is supposed to keep the plant smaller and sturdier and not quite as tall.
Another tip I have learned from a plant propagation class is that when you want to harden the plants off, you need to reduce the watering of the plants. You want them to dry out between watering.