You can use "alsjeblieft" or 'alstublieft" but more common is to say "graag gedaan" (= you're welcome) or "niets te danken".

both are correct. "alstjeblieft" is less formal and used to respond to "dank je", "dank je wel", etc. "alstublieft" is formal and used to respond to "dank u", dank u wel", etc. "alstjeblieft" and "alstublieft" are modern versions of the old Dutch "als het je/u belieft", which means as much as "if it pleases you". The two other responders gave you alternatives that would be more appropriate to an informal setting, although "met plezier" might be used formally under certain circumstances. I find Rosetta Stone very useful, it's good for repetition and to practice your pronounciation if you don't have someone to help you in that area.

Less common, but another alternative is to say "with pleasure": "met plezier".

You could also say "geen probleem" (no problem) depending on the context.