How to use GET/POST in xwiki

I have a question regarding the use of GET/POST in xwiki. How do I send to a velocity script a string using GET or maybe something similar (like $context??) in xwiki? I read something about xwiki context, like getResponse() and getRequest(), but I would like an example to understand better, because the api is very lacunal. Thank you. Evelina Slatineanu