Contact a loca running club. They can get you started. You can train for distances up to a half marathon by yourself in your neighborhood. For a full, it's better to train with a group mainly for the longer runs.
I train with this local group each year. Sportbackers is the organization that produces the Richmond races. Supposedly, they had around 1900 total runners(counting the vitrual and walking team) split into the various sub teams last year. That's a 23 week program. You can look at the training manual to get an idea of the training load.
https://www.richmondmarathon.org/mar...training-team/
https://www.sportsbackers.org/traini...training-team/