Standard form writes a number as $a\times 10^n$. The coefficient $a$ must satisfy $1\le a<10$, and $n$ must be an integer, so it can be positive, negative, or zero.

Positive exponents make numbers larger and negative exponents make numbers smaller. The exponent tells you how many places the decimal point has moved.

$4.6\times 10^8$ is in standard form, but $46\times 10^7$ is not because the coefficient is too big. $0.48\times 10^5$ is not finished either, and it should be rewritten as $4.8\times 10^4$.