Most girls I see are college students and I'm not able to approach them to start a conversation, most of them walking, specially cold aprroaches.

What can you recommend me to gain more confidence and be able to start a conversation to someone that I don't know?

For example, if I see 2 girls in a bench in a sunny day, or simply taking a walk, what would you recommend me to gain confidence or phrases can I use así openers?

My biggest problem is that they could think that I'm bothering them or I'm stalking them or something like that (Here in Spain feminist movement is too strong and simply everything you do can be misunderstood).