Creating italic version?

How can I rotate a glyph? I want to keep the current vector path, I don’t want to change the shape, I just want to rotate it to create an italic version. :c

Do you want to rotate or slant your glyph? I suspect the latter if you want an oblique/italic. In this case, read this:
http://glyphsapp.com/blog/easy-oblique/

Transformations can be done via Filter > Transformations (works on complete layers), or via Palette > Transformations (works on partial selections too).