Hi - and welcome!
There are 2 answers to this
The first is that seeing any species is a combination of choosing the right location and date. For more explanation, see the FAQ at
http://www.ukbutterflies.co.uk/faq.php.
The second suggestion (which is simpler) is to visit a local nature reserve. Most are very accommodating when it comes to butterflies.
Out of interest, whereabouts do you live? That would help pin down some location sites for you.
Cheers,
- Pete