These 2 particles は wa & が ga both do what in English is the
subject, but は wa is greater in scope than が ga  wa - the main
topic particle of the conversation  ga - the subject particle of
the sentence  わたし　クレイ　です。 watashi wa kurei desu. I am Clay.
[Clay is the topic and now this is known, it won't be repeated
unless the topic changes]  ねこ　すき　です。 neko ga suki desu. (I) like
cats.   ["cats" are actually the 'subject' here.  Maybe this is
easier to see "Cats are liked (by me).  Note you could say
"watashi wa neko ga suki desu." but it is unnecessary because we
have already said "watashi wa" (The overall topic is already
known)]  if both are in a sentence, the wa is first   the wa is
written with a hiragana ha but pronounced as wa