You did not specify, but I am guessing you are referring to vegetables rather than flowers. There are a couple reliable websites with information about starting seeds indoors and how to do it. Depending on the plants selected the time to start seeds indoors may vary due to the time of germination in conjunction with frost free dates when they can be transplanted outdoors. The most common time to begin indoor seeding is late January to February.

https://u.osu.edu/knoxcountyag/2018/03/21/a-beginners-guide-to-starting-seeds-indoors/

https://bygl.osu.edu/node/2309

Herbs, such as oregano, parsley, chives, thyme, rosemary, lavender and sage may be started indoors also.  

Flowers: Dusty miller, Snapdragons, Geraniums, Begonias, Pansies, and Delphiniums are appropriate to also.

I wish you success in starting seeds indoors with the result of an abundant garden this upcoming growing season.