Can I delete questions on here?

can I delete questions I have asked? if so, how?

No, you can choose to make then anonymous though.
You do that by going to your profile, click 'My Questions' and on that page you can choose to make any of your past questions anonymous. Questions only get deleted if they go against the terms of use. Also sometimes if a user gets nuked, their questions, comments, advice, etc. sometimes get deleted as well. Reason being, users being able to delete legitimate questions could really mess up the search engine. When a question gets marked anonymous it gets sent to 'fau' account or 'FunAdvice' account.