This page refers to the UK but you might still find some good general advice:
https://nationalcareersservice.direct.gov.uk/advice/planning/jobprofiles/Pages/actor.aspx
Nearly all of the young actors who appear on TV, or who get film roles, (certainly here in the UK) attend specialist performing arts schools. Many of those schools are full-time (and it's usually those schools which casting directors look first to recruit from) but there are also evening and weekend schools as well.
Even if you weren't able to get a TV or film part as a juvenile (and probably only about one in a thousand young actors ever do), joining a local drama group is almost certainly a very important thing for you to consider.
For example, if you were to later apply for a performing arts course at university you'd almost certainly be asked what experience you'd already had.
If you could list the parts you'd played in your local amateur dramatics productions and tell the university admissions staff about the associated work you'd done helping out as stage crew and with lighting, as well as mentioning things like dancing and voice training, you'd be in a
far better position than simply having to reply 'None at all'.