Ghusl janabat ya koi bhi aur ghusl tartibi lena shower se jayaz hai? Directly stand below shower and wet the body in three parts?

You can do ghusl under the shower however Ayatullah Sistani says first wash the head and neck and then the body. If you stand under the shower and make no movement, it is not correct. As per Ayatullah Sistani, it is ihtiyat wajib (obligatory precaution) to make some movement to make it clear that you are now for example washing the body.