It is not possible to talk exclusively to girls on Omegle, as of 2015. When using Omegle, the app randomly selects a chat partner and there is no way to pre-select a preferred gender.
Though users cannot filter by gender, Omegle does offer the ability to type in interests before a chat starts, in order to help find other users who share similar tastes. Those using the app can also choose between text chats and video chats, and a college student chat is available for users who verify that they are in college.
Users on Omegle are anonymous unless they choose to identify themselves to others. However, though self-identifying is an option, it is generally a good idea to observe internet safety protocols and never give out personal information to random strangers.