Me Gustarķa... is the conditional form of gustar... to like/to please: literal translation: "it would please me"
Quiero... is "I want"
Quisieria: is the conditional form of to want... the actual translation is "I would want/like".
If you want to order something, other ways to say this are:
- dos cortados, por favor
- me pones... una tapa.... put me a tapa. I've been listening, and that's often how they ask for something here.