When you like a girl, you show it by flirting a lot with her and trying to make her feel more special than other female friends that you may have around. You also can hold hands with her when walking around. Spending time with her is also a good thing, so you can get to know each other well and this can be through asking her out.
i dont flirt, dont make it too long just come up to her and say hey pretty, i like you, can i get to know you better? phone number maybe whats your name, how old... and it goes last week i did that and i got a girls number