# blank spaces in a new line

I want to add some blank spaces to my margin when i go to a new line.
The second " = " sign should be just below the first " = "
How can i do that?

You are looking for environments provided in the amsmath package. Here, I use aligned to make certain tab-points align at the & tokens. In this case, the equations are not numbered. If you need numbering, use the align environment without the surrounding $...$ delimiters.
\documentclass{article}
\begin{aligned} f(n) &= \log(n^n)^3\\ &= \log(n^{3n}) \end{aligned}