Learning Numbers in Japanese Language (01 July 2023)

Today, i try to learn Numbers in Japanese Language. Here what I learn today 01 July 2023:

One : ichi
Two : ni
Three : san
Four : shi / yon
Five : go
Six : roku
Seven : nana / shichi
Eight : hachi
Nine : ku / kyuu
Ten : juu

Thats what i learn today, but i dont know the different between shi and yon, nana and shichi, ku and kyuu. Does here anyone help me to explain these?

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