Explanation about は and が as subject markers

[sugoiAngel07]

Thank you so much, it's really do make sense.

[ColbaltFire]

This is the least viewed video on wa and ga and it's probably the best. Thanks!

[metaphoricrocky]

I forgive you for that video being a little bit weird.

[bluetube147]

can u explain this to me im having trouble understanding when ga and wa is used i heard wa is used when talking about the topic and ga for the subject and i thought i got it but now im confused again so lets say you wanted to say i am john- watashi WA or GA john desu i mean if you used wa its talking bout the topic and ga the subject soooo its confusing i know your supose to use wa in that sentence but why?