I know that Ctrl + N is to find classes and it is very useful. But what about methods?
If you click on a method, you can do Ctrl + B to go to that method's declaration. Similar to F12 in MS Visual Studio.
Ctrl + Shift + Alt+ 7 after selecting the method
Ctrl + Alt + Shift + N allows you to search for symbols, including methods.
The primary advantage of this more complicated keybinding is that is searches in all files, not just the current file as Ctrl + F12 does.
(And as always, for Mac you substitute Cmd for Ctrl for these keybindings.)
If you just want to look for methods:
On mac OS X 10.5+ binding, it is Alt + ⌘ + O
By Default XWin Key binding, it is Shift + Ctrl + Alt + N
You can also press double SHIFT then, you can search anything (not only method, but also class, files, and actions)
Intellij IDEA 2017.3.4 - 2018.2 (Ultimate) on OSX
CMD + fn + F12
will show all members of the current class in a popup window, then you can search method in that class.
BUT, this answer is depends on your Keyboard setting. If your keyboard setting in
System Preferences > Keyboard > Use all F1, F2, etc. keys as standard function keys
is selected, then the shortcut becomes
CMD + F12
Slightly beside the actual question, but nonetheless useful: The Help menu of Intellij has an option 'Default Keymap reference', which opens a PDF with the complete mapping. (Ctrl+F12 is mentioned there)